Would you vs. will you?
'Would you' questions almost always fail to evoke useful information. That's because people are nice, and want to spare your feelings. "Sure, if you built x, y and z, then of course I'd consider buying it."
On the other hand, 'Will you' questions get to the truth immediately. "Yes, I'll buy that from you today."
You can do all the research in the world, but until you have the guts to make a sale, it's difficult to be certain of anything.