Any metal aircraft's biggest enemy is corrosion & without going into too much detail there are a few common places where you can look for it on the 150 yourself but I'd recommend that you have a qualified person examine it.
The rear spar carry through which will necessitate removing the hood lining or plastic panelling depending on the model. Look for white powder on the roof panel where it contacts the spar & around the brackets that attach the carry through to the rear pillars.
The wing main spar has an extrusion which is prone to exfoliation corrosion & you'd need to remove all the inspection covers under the wing to have a good look at the spar with a strong light.
The nose skin & ribs, remove the landing light lens so that you can see down inside the skin with a mirror
Exfoliation of the gearbox mounts for the landing gear, remove the cover where the gear leg enters the fuselage & the bulkhead covers behind the seats so you can see the inner & outer mounts.
The list goes on but if these parts of the airframe look to be in good condition then get an A&P to look the rest of the aircraft over properly. It'll probably cost you a full days labour if done properly & he'll check for things that would also normally be inspected on an annual like worn cables, seized pulleys, whether all AD's have been complied with, leak down test, log books etc etc.
I don't consider this to be a definitive answer to your question but hopefully a possible starting point.
Regardz
DJ
Never argue with a fool, onlookers may not be able to tell the difference.
