I would like everyone to consider that it is very easy to inspect a wheel bearing. A good trusted shop can inspect them very easily. If you are capable of removing a tire you also are capable of inspecting them.
I recommend that any used trailer purchased have the bearings inspected. I did not do this on a boat I bought. Everything was well maintained but I toasted a bearing and needed a new axle. I was also in the sticks so it was costly.
I also hear about new trailers having metal shavings when inspected or other indicators of a bad install. For this I recommend a temp gun or putting your hand on the bearing to feel.
I recommend making sure you check the inner bearing as well as the outer. You will be able to feel an issue before it happens. I have extra sets of bearings in case I have an issue and it takes about 20 minutes to replace the bearings and races. This is not a hard job to do at a rest stop or campground. It is even easier if you have a new hub with greased bearings already. It is almost as easy as a tire change.
Paul