If I respond to a tech recruiter inquiry and say that I'm open to hearing about other opportunities, but only so that I can learn more about what other companies are offering for compensation, to get practice on interviews, or to scout other companies to hire their developers away...and have no intent whatsoever of accepting any other offers, is that unprofessional, or is it being clever and using my resources to learn more about this hiring environment?
Yes, it's unprofessional to lead the recruiter to think that you are genuinely interested in a new position when you know you are not. It's getting them to advance your interests without being honest with them about the odds of them getting compensated for their time and effort. How would you feel about a software company that got free consulting services by bringing in applicants for a non-existent position and having the applicants solve "test" questions that just happen to be real engineering problems?
Just be honest and open with the recruiter. Let them know that you really aren't interested in a new position, but are interested in finding out about compensation levels for someone of your skills and interests. Some recruiters will immediately drop you, but others may be happy to work with you. They know that if you are asking the question, then if they find a really sweet deal for you, you are going to be tempted, no matter what you say now. The key thing is that everybody knows the score, and nobody is being deceived.
Recruiters get paid on commission. If they know you won't change jobs, they have no incentive to shop you around. If you lie to them and tell them you are interested only to poach employees for other companies or gather salary information, then you run the risk of getting a bad professional reputation since you are lying to gather information. If you want to play the field, play the field, but be honest about your intentions.
No Pay, No Play
Recruiters usually get X weeks/months of a new hire's salary when they find the placement. If you tell a recruiter, "Yeah, I want to see my market value, poach employees, and get some interview practice" then the recruiter has zero incentive to help you out.
So feel free to tell a recruiter this, but realize it is a way of telling them, "Go look elsewhere".
No Honor Among Thieves
But let's say you still want to shop around anyway. So you lie about it. You say, "Sure Mr. Recruiter, I would love to see what's out there! Send me all the opportunities that you think are a good fit!" but end up refusing seemingly good placements, you are going to get caught soon enough.
Let's say you are introduced to Company A. You have a phone interview, they call you in for an in-person interview, and they really like your style. What do you do if you get sent an offer letter? The company assumes you are negotiating over terms at that point. The recruiter assumes it's a matter of money. The more successful you are, the more quickly you will be caught.
Company A may put you on a blacklist. So might the recruiter. And depending on your industry, if you're really looking for a job in 5 years, you may find doors shut to you because they assume you are just on a fishing expedition again.
Be dishonest at your own risk.
Everyone Has Their Price
Yet there is a wonderful middle-ground. If your dream company called up and offered you any position you like at double what you think you're worth, would you take the job?
If so, you can use the recruiter to help you find that job. It may not be out there. There may be false calls. But at least you are honest with everyone in the process. The recruiter may think you are too picky, and may think you are asking for the world and give up on you, but at least everyone knows who is out for what.
You say you "have no intent whatsoever of accepting any other offers", you may want to re-evaluate your stance to, a more moderate position such as, "I have no intent of accepting an offer that doesn't represent significant benefits in areas A, B, and C over my current position". Telling a recruiter that will cause him to decide to raise to the challenge, or look for someone easier to convince to change jobs.
There are always more recruiters, your reputation is a bit more permanent.
If in today's world of tech you go wasting time of recruiters on telephonic and face to face interviews then its unprofessional. If your idea is just to gather information about whats in demand and whats being paid in the job market then i think you can very effectively use internet without wasting any body's time. Apart from that if you are good and you clear many rounds and then say no, I have to say buddy you are actually causing loss to the organization because each round costs in terms of resources and money and most important delay in hiring the required resource.
I will give a example "Some one has head ache he goes to hospital, doctor examines him talks to him then say sorry i am off duty "..you are being that doctor.
If a recruiter calls you after viewing your profile. Then seeking all information about what they have to offer and then saying no should be ok because it was not you who proactively approached them.
You may be making two assumptions that you discover aren't true: first is that your skills are not much evolved from when you started at your present job, and second that that compensation picture hasn't materially changed. I'm seeing ads on social media boards that are trumpeting $50,000 upgrades for certain development roles, which I'm figuring means someone getting paid $80,000 will now make $130,000. So your 'fishing expedition' might hold some surprises.
It's up to the recruiter to determine whether you're wasting his/her time. I've had several meetings with recruiters that I first connected with on social media - we had cordial conversations but I pointed out I wasn't in the market and not interested in the kind of employers they were recruiting for. If you find out the job market has improved, and you happen to know someone that's ready to jump, the recruiter will be more than happy to pull the ripcord.
It's unprofessional , but mainly it is a waste of time which is why it is not clever. You might get some salary ranges, but nothing like an offer until several interviews. Many jobs are posted online. I don't know if there's a huge discrepancy between requirements for jobs that go through recruiters and those that don't. Maybe for senior executive positions.
How are you going to scout other companies during this process? You plan on wasting an interviewer's time and then offer him/her a job?
Why aren't you involved with local groups in your profession so you really know where to find the best tallent? I think most recruiters are a poor judge of talent.
You asked a good question but most of your situations are nonsense:
to get practice on interviews
It sounds absurd that you would take a vacation day and spend a day with a target company for the kind of mock interview practice you can get on your own, and keep some sort of poker face through it all. This is a farcical example.
to scout other companies to hire their developers away
Aren't there less circuitous ways to do this? Maybe you should ask the recruiter if they want to hire you?
If I respond to a tech recruiter inquiry and say that I'm open to hearing about other opportunities
That's reasonable. IMO if you're clear about your intent with the recruiter, they can spend their time with you as they please. Some will work with you a) because they think you're more poachable than you realize, or b) because they want you to give them a call down the road when you really are seriously looking. But I've taken a call in exactly this situation and the recruiter was basically flummoxed that I wasn't ready to start interviewing, and I definitely made myself clear on that point. But that's the business.