what I give in US-restaurants (don't do this in Switzerland - you would spoil our system, tips are included here so please only round up) is about the 15-20% preview travel recommends - but beeing lazy (to calculate) I just write it on the credit-card into the tip-column in % (f.e. 16%) and leave the total open.

Questions:
- is this acceptable?
- is it dangerous? (that way I leave the toal open, but I see little danger as long as these bills are at the hotel-resaurant or bar, I can still discuss the matter at check-out-time, when they present the summarized bill - never had to till now)
- will the owner give the credit-card-tip to the employee? (will he deduct the 3-5% credit card commission from that tip amount? should I pay the tip practically always in cash? paying cash do I help to "cheat" the income-tax-system of that state, country? etc, etc).
- how do I/you tip if on the bill/credit-card-slip there are two tip-columns ? (headwaiter and waiter?)
- is it acceptable if I/we deal with my/our luggage my-/ourself? (for not taking risks, but also for not having to tip).