My situation is a little different than many - language and ability to read is an issue where i am. Things also must be as simple as possible in every way - eliminate extra steps. Use emoji, universal images as much as you can and the common language of the area.
You may or may not end up getting calls from customers 'pissed off' that your place ripped them off by charging them the max which is actually the preauth amount .... often what happens, especially with the advent of third party security systems/carriers for most
credit card companies .... the third party company flags or does not release the preauth quickly or flags a double charge so it may show up as an additional charge at their end for a bit. A phone call or text usually sorts it out and patience of a couple of days in almost all cases. This one is a few years old as my new signs include the qr code and a bit more info .... it is 24" x 24" .... hope that helps .... my top end is high as I have a few people who wash heavy equipment that require that time .... rural.
