In a lot of cases a "gently used" AS is one that was used for a while and then went into storage for many years. One would hope it was indoor rather than outdoor storage
There can be a wide range of "last replaced XXX " dates as a result.
A 2008 will be roughly 14 years old when you get it.
Batteries last about 5 years so it should have had them swapped several times. It's a pretty good bet you will be putting in new batteries.
Tires at 14 years are well past their "use by" date. Often a "prep to sell" process puts on the lowest cost tires they can find. Those are *not* the tires you want on your trailer. Budget for new ones. If you get lucky, that budget money goes into the camping fund
Brakes likely have been replaced if the trailer did see use. This one is a wild card. Budget for it, but don't count on it.
Wheel hubs are in the same category as brakes. They do need to be lubed regularly so who knows ....
The sealing goop that keeps the rain out of the joints between the roof and stuff like the A/C unit probably isn't going to last 14 years. Having somebody chip off all the old stuff and re-do it isn't cheap. Sorry about that ....
Window and door seals are going to depend a lot on just what sort of use the trailer saw. Seals on various plumbing items are in the same category.
As noted at the start, you really don't know how much of this has been taken care of and how well. An inspector can give you a reasonable idea on most of it. He also can dig a bit into things that fall more into the "needed repairs" category. Everything above is what I would call routine maintenance.
Why go through this now? My *guess* is that a trailer in perfect shape will be selling at a crazy premium. Used trailer at new trailer price is not anything *I* would be interested in ( Indeed that was a choice I was given a couple weeks back ). You may well do better to buy a trailer that has some maintenance needed, but not much repair on the list. Far easier to research the cost of this stuff in your spare time than to do it all as part of a 20 minute decision process.
Repair wise, water damage and floor rot is the big risk. It can be hard to spot. It's not cheap to repair. Any A/C unit that is 14 years old is suspect. If it's still working, fine. Figure there will be a replacement in your future. To me minor damage to panels (a dent here a scratch there) is inevitable. A full repair can involve pulling off the existing aluminum and replacing it, that's not cheap. I'd plan on living with whatever (hopefully minor) scratches there are .... There are a lot more things that *could* be in the repair category.
Have fun !!!