well 1. some restaurants take the bill and auto debt 20% to see if the $ is available on the card and then Reverese it out later.. usually this will take 2-3 days..

if it is anything after that.. hmm yea they did stiff you. Do what I do when I tip

write $5.00 then under it put Five dollars in writiing and sign it..

this way your yellow copy will have both the 5.00 and it written out so it is very hard to dispute