I would assume that all agreements are something that can and will be broken. The only thing that works is make them put their money where their mouth is. If they are serious about acquiring you, they must be prepared to spend money to do it: lawyer fees, accounting fees, and money paid to you in exchange for your company. So, make sure there is money on the table: a non-refundable termination fee, which could be a percentage of the theoretical purchase price. I went with 5% with the sale of my company.

A good salesman will never put a price out there first, so you will probably need to come up with that valuation: just put it out there high enough so you will be happy were it to go through, and assume this is the beginning of the negotiation. If you and the acquirer cannot get close in that discussion, this is a good gauge of future success in the other more complicated discussions that will come.

As others have said, get a good lawyer. There are lots of places where this can go awry. When I sold my company (~$450k), I did not understand the difference between an asset sale and a stock sale which has vastly different taxation implications. A good accountant is worthwhile here as well for the same reason.

You can tell them you cannot engage in a detailed discussion without the termination fee conversation completed since you will be spending money as well.