Almost all Golf Galaxy locations actually have a PGA member on staff. Not that that guarantees they are a great instructor or anything, but the couple Pros I know from around here that work at the various Dick's Sporting Goods and Golf Galaxy locations are great guys, and very good instructors. But, if the other guy you mentioned does a lot of teaching, might not be a bad idea to work with him.
With instructors, sort of like clubs, it is just as important finding one who you feel works well, not just the one who has the best certifications. My dad is a Class A PGA professional, but I couldn't stand working with him growing up. He is more of a "feel" player, and his instructions for me, more often than not, were just too vague and general. He's a great player, but I like to be more specific with my methods and instructions. So, I worked with the Assistant Pro at the club instead. He and I connected on very much the same wavelength with our swing thoughts and direction, so it was a great fit.
So, see how it goes, but don't hesitate to move on if you feel like the connection isn't there. Once you find an instructor who can communicate things in a way that makes sense to you and your swing thoughts, you will find your swing improvements coming much more frequently and naturally. Good luck.