If you buy fabric and other quilting items from that store, then go ahead and sew there.
If they don't already have classes you may start a trend for them to do so. It is to they're advantage to have you there. You help them show how much fun quilting can be and thus help them sell more fabric and such. You also show others how much the store personnel will help them if they need it. You become free publicity for them.
If you still feel awkward ... take them a homemade cake or something you all can share.
A LQS without any quilting activity is usually a store I would avoid.
ali