It isn't over until the contract is signed. Until that point, everything is negotiable. There are generally 3 stages to any contract negotiation:
- Conceptual Negotiation
- Detailed Negotiation
- Uh-oh Negotiation
Almost any negotiation starts conceptually:
- What are the deal-breakers for both sides?
- What things are more/less highly evaluated for each side?
- What will the general process be to close the deal?
Since the parties negotiating generally don't have the last say in the decision (they will need approval from someone), these are not firm promises, but closer to a Memorandum of Understanding. Basically, you are setting up the playing field for negotiation (e.g. "the boundaries are from this tree to that lamp post, and there will be no elbows thrown, and when you're out you need to give someone else a turn").
This is what you just did with the interviewer.
In the conceptual negotiation, the interviewer said that the company couldn't offer the salary you wanted, but you said that was okay as long as you get benefits to make up for the lack of salary. You agreed you would take the job if they provided an offer that met those expectations. If, for instance, the gap between the salary you wanted and the salary they offered was 10%, and they only offered 5% of that gap in benefits, then you are more than in your rights to press them to up that to 10% -- that was what you had discussed conceptually.
Or if they wanted to provide benefits you didn't value (such as transportation allowance when you live within walking distance of the office), or a gym membership when you believe treadmills are a sin against humanity, you could negotiate the details of those benefits so that they are equivalent to the 10% gap in salary.
Detailed negotiation may also include certain contract clauses. Maybe there is a non-compete clause, or a confidential information clause that would prevent you from ever working in the same industry. Maybe there is a 6 months notice period or something of the sort. All of these things are not monetary, and aren't discussed in the conceptual stage, but are definitely very important parts of the contract that need to be discussed.
Most negotiations only have the first two stages. But there is a very real and important third stage which comes up more often than it should.
Sometimes one party will think, "Now I have them where I want them" and use the opportunity to try to extort more out of the other party. For instance, if the company assumes they will sign with you, they may have stopped pursuing other candidates, by pushing more demands then the company may be in a worse situation to negotiate. On the other hand, if the candidate assumes they will get the job, they may have turned down other offers already, and may be in a weaker position if the company offers less than they conceptually agreed to.
Note: I strongly discourage this type of behavior on all sides, but it happens more frequently than it should
The company could hit a rough patch during the process and find they don't have the budget to offer the salary/benefits they promised you. Or maybe the employee has a family emergency that requires him to move out of the area. Or any number of scenarios that make the agreement as conceptually negotiated fall through. Or an earthquake hits. Or the bubble bursts and cash flow stops. Or...
This is another reason why it isn't over until both parties sign the contract.