Check the sump over for any possible cracks, same with the skimmer.
Not sure if internal overflow or what. I would not get a tank with a vacuum started overflow box (old school) but either internal or drilled overflow.
Look at the tank seams and make sure they look the same, a visible difference in the appearance of the sealant could indicate sealant separating.
From the full tank shot it appears there are shims under the front to level. If so, that is good, because it is very important to keep tanks on a solid, stable and LEVEL surface. Only issue I have with the picture is the shims sticking out, I would think if they have been there since set up, the owner would have trimmed them.