Steve
A couple of important things to check on a new or used trailer are the load rating of the tires and axles and how the vehicle tie downs are fastened to the trailer. Believe it or not, I've seen some pretty nice trailers with D-Ring tie downs fastened with four wood screws in the plywood floor. Guess what happens during a panic stop? Going up in tire rating helps lower tire temps and lesson the chance of blowouts.
I ordered the trailer I wanted and didn't worry about resale. Let my widow decide if she wants to sell or not. We have a Pace American gooseneck type 20 ft. box with that great extra storage area over the hitch. We added a side awning and drivers side door, and an electric winch. We have two strips of E-Track for securing cars to at any point. They work great for different length cars. The interior is all wood. Our trailer has the wider width. Before our purchase, several trailer owners told me to avoid tile or diamond plate in the wheel track areas because the cars will "scoot" sideways easier. I think our trailer is a "Shadow" model. A gooseneck trailer may be a little higher priced than a straight hitch, but 4 years ago we paid around $12500.00.
Once you spec out a trailer of a certain length, adding extra feet of length is not that much more. If you plan to haul anything bigger than Cobra sized, I definitely recommend a 20 ft. box. Keep in mind that the longer the trailer is, the more room you need to turn around, especially in dead end Hotel parking lots. Not all hotels have parking lots that circle the building.
Happy hunting.
Fast Farmer