Be careful of Restaurant.com. I bought a $10 gift certificate for Mongolian Grill in Mukilteo for $4. The place only does counter service, but insisted on the 18% gratuity in the fine print, basically eating up the entire savings.
The restaurant justified it as they needed to make back the loss they were taking on the gift certificate. I had to make 4 trips to get the food and drinks for my wife and kids to the table, and they couldn't even be bothered to offer a tray, but they felt they were entitled to an 18% tip because they gave me a discount that the tip eliminated.
And Restaurant.com basically said "well, we state that they can charge the tip" and if I didn't like it, I could scan through their listings to find the 6% of restaurants in my area that do have offers with them, but don't have the fine print about a gratuity. I say "scan through" because, of course, they don't actually let you sort or search by that criteria. If I want a restaurant that doesn't have a mandatory tip, the selection of deals in my area goes from 76 to 4.
I don't mind the 18% at a sit-down restaurant where I'd tip around that much anyway. Maybe I'd be out an extra $2 if I felt the service didn't rate a full 18%. But letting a self-serve place, where there's NO service to speak of, tack on the 18% and telling the customer it's "buyer beware" is bull. I'm never going back to that restaurant and Restaurant.com is never getting another penny from me.