What happens if seller delays closing?

You need to speak to your attorney about this. Terms of your contract are no doubt extremely specific on these points and it is exactly what a real estate attorney deals with.

How could you have incurred "extra costs" already?

If the seller has a contractual closing of July 15th you are a little early to grouse about the situation.

Unless the contract specifically states otherwise, a "reasonable delay" is allowed. Now that term is subject to interpretation but most of the time a 30 - 60 delay would usually be seen as reasonable.

Write back in September if the Seller has not closed.

This happened to us, and it is exactly what the real estate attorney is supposed to deal with. Our attorney had back-and-forth with the other attorney to try to nail down a specific date, which kept being put off again and again. If you are truly nervous and think the seller may not come through, you might want to try to get your deposit back so that you can move on to another property. That's what we were finally forced to do.

I should have clarified--the contract closing date was June 15 with a specified 30 day window.Amity95, did you recoup any of your fees (lawyer fees, application fees) from the seller who backed out?