Always Read the Fine Print

I'm not going to name names, but I saw an online offer for a local pizzeria for a $10 gift certificate for sale for $5. The fine print notes that there is a minimum purchase of $20 and that an 18% gratuity is added prior to discount.
So let me get this straight - you pay $5 for a $10 coupon, for a net value of $5. If you spend $20, they automatically add $3.60 to the bill. So you're down to a $1.40 savings. And every dollar you spend over $20 will lower that by another 36 cents. Not much of a deal.
And anyway, what's with an 18% "gratuity" at a pizzeria - with counter service, yet?!