A new axle
is $600-800 installed, and you end up with a brand new axle, good for another 20 years or so, and you can add brakes
, a major safety upgrade lacking on many vintage 13'ers. It's a fairly straightforward replacement. If the price reflected the need for a new axle, I wouldn't necessarily pass on an otherwise nice trailer.
A better way to check axle arm movement is to bring a small floor jack with you when you inspect (you'll need one anyway as a trailer owner). Jack up the trailer on the frame near the axle and watch for the axle arms to drop an inch or two.
A rotten floor, on the other hand, is definitely a reason to run!
Trilliums have a fiberglass-encased floor, so feeling for sponginess is the only way to check. A lot of other brands do not encase the floor in fiberglass, so you can inspect inside cabinets (where the sub floor may be exposed) with a flashlight and screwdriver. Look for water stains and tap around with the handle of the screwdriver listening for soft spots. Pay special attention to the outer perimeter under windows
and wherever there is plumbing. With some brands you can look underneath as well, if there isn't a layer of fiberglass on the bottom. Again, look for water stains and tap around for soft spots.
Based on Kai's experience, brand new finish flooring in a trailer is a signal to be extra cautious. What are they trying to conceal? Most folks wouldn't install brand new flooring right before selling.