Most travel trailers have cheap tires on them. If you look closely at the specs, they are speed rated at 50 mph. Do yourself a favor and look up the ratings and reputation on the tires. You can usually use this as a negotiating item.
Although typical trailer tires are ST tires, some of the higher end trailer companies will install light truck (LT) tires on the trailer. I have found LT tires to be a much higher quality option than "most but not all" of the ST tires.
There is a big difference in quality amongst travel trailers. Many of the inexpensive ones develop problems after a few years. The higher quality ones don't.
Look closely at the sizes of fresh water, grey water and black water tanks. Bigger is better if you intend remote camping. Also look at how easy it is to do routine maintenance, such as ease of access to the water pump, etc. Check the water system to see if it has a drain installed at the lowest point for winter draining.