Depending on local custom, the buyer may or may not see the seller's expenses.

Put a sign in the front yard (like the Realtors use) cost about $70 to make a custom one with the sign and frame.

He lets me "sandbox" custom codes in different regions just to see if it will work... for free.

As a last resort if the window is a custom design then this would be the worst option since you will need a custom ($$) replacement.

This however will become evident when you actually see how your customized set of numbers work out, and compare the result to what is necessary to achieve your personal financial objective.

These customers are narrowed to a particular brand and model.

I suggest you talk to an attorney in your area as local custom and state law will have an important role in setting up the tactics of this deal, IMO.

Have you ever looked into buying a customized handwriting font for your computer?

It makes easier to formulate some questions.A spur of the moment opportunity gives little chance to prepare, but I wouldn't let that stop you from asking general questions and/or specific questions based on what you do know.Open ended questions are always good.

If you are in California it will probably cost you a few hundred to set it up IF you just have a generic template which may defeat the purpose any ways since you need to customize it since there are a few of you.