1923-S SLQ On Ebay

I am definitely no expert on these, but that mint mark stands out as a big warning to me. Looks like it has been added. The area around it simply doesn't match with the rest of the coin.

Stay away. Added S for sure.

Real or not I would not be comfortable with that coin at all.
The circle around the "s" sticks out like a sore thumb.

Johnny - I'd contact the dealer before buying that one. Definitely a red flag on the MM. Let us know what he says.

MM position looks too low and not consistent with the wear of the rest of the coin

I had a 1923 S Quarter in EF, which I picked from a 50c junk box once. That was in 1984. I sent it to auction about a year later, where it realised $50. I wasn't into American material then, my love was and still is ancients. We were changing houses at the time, and I needed some spare money to pay conveyancing fees.

Hindsight says that I should have kept it, because I now have a small American collection of perhaps 100 coins including some nice gold.

Actually, that is really common on both the 1923 and 1923-s. The "192" almost always wears faster than the "3".