Generally you cannot use Restaurant.com 'certificates' for shops because they are considered "coupons". From time to time Restaurant.com has had really good sales where a $25 certificate is only a buck or two. I load up at that point because if we go to the restaurant once and it wasn't interesting, I can always swap my $25 certificate for some other location. There are some locations here that fly off their board so forget getting them when they have a good sale. Swapping one of my old certificates for one of those locations when I see them allows me to make my own 'sale' on them.
Generally the restaurants that offer through Restaurants.com are either brand new or are struggling to survive (usually for good reason). So they give us an opportunity to try new places and if one we buy goes out of business before we get there, we just swap for something else. The other aspect is that we are a winter tourist area so the Restaurant.com certificates are something to load up on out of season here and then call before going during tourist season to see if they are still honoring the certificates.