^^^ You could take some measurements to check the symmetry of the frame. Use a string or a straight edge to see if the seat stays are straight or if curved then ensure they are symmetrical.
Measure from each base of the bridge to its corresponding fork end (dropout).
Also (and maybe do this first) check the rear fork ends to make sure they are aligned. This is easy to do using a a couple of pieces of all thread attached to each side, they should point at each other in the middle.