It can get a bit wearisom answering one question after another. Ideally you should aim to ask all your questions in batches, but if the answers lead to more questions...
A common problem. The respondent is either illiterate (quite common these days) and is possibly embarrassed about it, or is trying to hide something. The indicator of the latter is that you ask 5 questions and he answers 4 of them, and avoids answering the 5th one in subsequent comms.
Very very occassionally somebody is just too busy.
The market is full of used planes. In general, it's a buyers market. I would look for another one.