I think your use of the phrase "far more" (and the example of 50% over market rate) is what people are reacting to in their answers.
Your "market value" is simply what an employer is willing to pay when you're stacked up against the competition.
Entry-level positions usually do have SOME room for negotiation, of course, and that varies according to qualities of the individual candidates, the choice the employer actually has, and their own policies. All of these things together can cause the amount of negotiation room to vary wildly from zero to quite a lot.
I do think that asking for a salary that is far beyond what you're willing to accept is risky, even for experienced candidates. You might not get the offer but you'll learn a hard lesson for next time.
There is a lot of advice here and elsewhere on how to handle the salary negotiation. In general all this is easier if they just give you a number that you can use as a starting point or accept or reject.
Sometimes, however, you find yourself in a situation where you have to give a number first. To handle that situation, you need to do some homework beforehand to find out what are the ranges for that job in that company (or others like it). It is best to indicate your expectation but leave a door open to flexibility (eg "I understand that the typical wage for this entry-level position is somewhere between 10 and 13, does this match what you had in mind?" )
The salary expectation question definitely will come at the end of the process if you've had successful interviews and they want to make you an offer. In that case, give a range of salary that you're willing consider. They may come back to you with something towards the lower end of that. If so, you USUALLY can ask for something more-- after all, they're extending the offer to you so they chose you. That can be worth a few percent at least, but don't go overboard with back-and-forth. One bounce is what I always do, some people get away with a lot more haggling, but there's more risk that they'll drop you.
If you're dealing with recruiters or HR departments, they will sometimes try to put the salary expectation question upfront. This is not the final negotiation, of course, but it can be used to screen out candidates who have salary expectations that don't overlap with what is budgeted for the position. When you answer this you definitely want to leave the door open as wide as possible for further negotiation. YMMV, but I always give a lower bound and indicate a strong desire to find out more about the specific position.