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.
I don't recommend them. You don't get the full face value of the coupon. There is also a purchase minimum to meet, so your meal might net you maybe 20 percent off if you are lucky, plus they add in an 18 percent gratuity automatically. My husband and I got these as a reward on a shop. They promptly went in the trash.
I used them for several years and like Flash bought a bunch when they were $4 for $100. I do not see those deals much anymore and since I mystery shop dinners a lot I really do not need them. Also in my market the restaurants still act like the recession is in full bloom and put 2 for 1 coupons in the paper frequently. I purchase the restaurant.com as a "gift" and then just convert them to the restaurant I want to go to on the day of the meal. I find them useful when traveling to a city where you know no one and have no idea what is good or bad. So far I have never had a bad meal thru them and probably have eaten in 20-30 places over the years.
I figure I am going to tip anyway. So we go to a restaurant and dinner is $40 so a 15% tip would be $6 and the dinner costs $46. Same scenario, $40 dinner with a mandatory 18% equals $47.20 + $1 for the $25 coupon = $48.20 less $25 certificate = $23.20. I have no argument with that because it comes out about the same as a BOGO. The restaurants here are definitely over 'recession pricing' so more frequently than not you will see a coupon that is more like $5 off $50 purchase.