Fair offer? For whom? I guess I look at these things a little differently. NADA, Kelly Blue Book and other "guides" are just a starting point. (They are currently very high and don't even agree among themselves) Things happen too fast and the numbers are not very objective for those guides to be accurate. Used car salesmen like to whip them out to low ball you when trading up.
You need to figure a price from what you want to pay and not what someone wants for his/her vehicle. A "fair" price will not be "fair" to both parties. He/she needs to sell and you may want to buy!
Another thing to consider is the scarcity of the item. There are more (and are going to be more) '05s out there for sale than '55s. Don't get into a hurry on hobbies. There is always another one out there unless it is something extremely rare.
There are two things to remember:
1.Trailers, motor homes, cars, trucks, motorcycles, boats, etc. make terrible investments. Keep in mind that you are going to lose money on the deal before it is over. It is recreation that will cost you money much like golf, bowling, or motorcycle racing. Also, they will always cost 2 or 3 times the money you initially expect to spend on renovation.
2. The best deal is at the buy and not when you sell. In other words, don't spend a lot and expect to get it back at the other end-you won't.
Fair price? In these times, I'd have cash in hand, show up in a tow vehicle, have an updated printed ebay list of similar models that did not meet reserve, write your short offer on a business card and be prepared to walk away. You might advise the seller that you cannot come back for $100 if he knocks it off next week. Emphasize cash in hand right now!
The seller wants as much as possible and the prospective buyer want to pay as little as possible. Fair? It cannot be fair to both so, I think, you should be nicer to yourself than the other guy.
"Turleen", the '57 Flying Cloud
Lone Jack, MO
"You better learn it fast; you better learn it young"-John Fogerty