I hate to tell you this, but your first mistake was asking them to hold it for you. That indicates that you have significant interest.
What you should have asked is if there is any reason if might not be there at the time you can get there.
Don't let them know how far you are willing to drive or anything else specific. If asked say that you think it may be what you want, but you will have to do a first person look.
If it is used, condition becomes EVERYTHING. Be ready to look at, retire to a coffee shop and talk about it and return. Then be ready to wave the cash of your first offer (if you still want that one).
Remember, sale people make money on sales. Always be ready to leave. A line I have seen used (and successfully) was that this was convenient today. Tomorrow will be less convenient.
Matt