That question is next to impossible to answer from your pic. You need to answer some questions to determine if it is a proof. First off, does it have a mintmark? If it does then it is not a proof. Next, are the edges squared off? Are the fields mirrored? Do the devices have more detail than a normal business strike? If the answer to these questions is "yes" then the coin may be a proof. From your pic it does not look like a proof to me. You should take it to a coin dealer and let him tell you if it is a proof or not. Edit - If it is a proof it would Grey Sheet between $95/$105 (Pr-60) and $210/$230 (Pr-65).
Three dollars is not to much to pay for a MS Merc. But as already stated your pic is poor and we need both sides to make a semi-reliable judgement on grade. Look for the swirl or pin wheel affects in the fields to determine whether this coin has been circulated or worse cleaned. The condition of the fasces on the reverse will also determine value. If you don't know what a fasces is or why its on this coin you should google it. Its wonderful knowledge for anyone collecting Mercury dimes. Then again if you like it, 3 dollars is a small price for happiness. Keep on Collecting!!! Allen
It doesn't appear to be cleaned. I can't see any mint swirling that would give it a big thumbs up from me as a MS (Mint State) coin, but it doesn't mean they are not there. Other then that I like this coin, no bad contact marks, no obvious damage. I see no wear on the obverse, the hair, wings and bottom braids look very nice. 3 dollars is a great price. Buy it!!! Just remember that without great pics, or better, seeing this coin in hand a positive assessment can not be made.
Looks like a polished coin that's been photographed with multiple diffused lights, but I could be wrong on both couts. Not a coin I would take a chance on personally.
I have a polished merc which I posted before Link and this does not appear to be so. Either way, for 3$ thats a great buy! (assuming you do purchase it, which I would)
This is a bad pic, anyways this is one of my Merc Proofs, the toned one....pic is from seller I bought it from