Many boats will have variances in production quality when they are hand laid, and this one looks thin right there where the light shines through. It's
probably fine, as "new" boats are often thin like this all over.
The thing here that would bother me is the fact that many (most?) A-30's weren't thin or known for "thin spots", and A-30's didn't rely on engineering to compensate for brute glass strength like newer boats do.
The good news is this is easily fixed - just add
epoxy and glass. The boat is solid, even if some spots are thin. You say he is asking 10k? Bring 2.5k in cash and make an offer of 2k and work northward up to the 2.5k, and be ready to take possession if he bites.
It's what I'd try if I was willing to buy the boat. From the looks of it and in this buyers market, 10k is ludicrous.