I also agree with:
1) Having it inspected by a professional. Can be well worth the cost.
2) Bringing along someone with experience.
Bring along a good flashlight for the inspection. It's not uncommon for used units to have black tank issues that can be taken care of but at at an addition cost to the new owner. It might be helpful to have some quiet time without the sales person around. For me I found it easier to think things over to come to the right choice for me. I almost walked away from my TT but asked for time alone.
As for not knowing anything about travel trailer remember that the Internet can be your friend. This forum is a great resource and you can find lots of videos online too. The best way to gain knowledge & experience is by using the trailer. Driveway camping is a good idea as you can find out ahead of time what you know and what you need to find out before hitting the road. The same with camping locally. Campsite neighbors are usually willing to help another RVer.
Great choice for "Living within my means" and camping for one...
2011 Salem Cruise Lite 20RBXL & 2011 Toyota Tundra Dbl Cab
Camping History: 45 Trips / 133 Nights / 3736 Miles
FRF Social Group: Campers of the West