In the US we tip 20% on full bill, including tax.
In Mexico we tip 15% on full bill. Mexicans especially the most wealthy ones, rarely tip above 5%. But here in an expat community with lots of US and Canadian snowbirds, 10% is the norm, I'd guess.
In the US , we tip a minimum of $5 if the 20% is less than $5.
In Mexico we tip a minimum of 40 pesos if the 15% is less than that.
We leave tips in US lodging at $5 a night at the end of our trip.
In Mexico we tip the woman who cleans our hotel room directly, each day (sometimes it's a different person). More often we rent vacation homes in Mexico and the owner will usually leave an instruction sheet about the maid, who they are, when they come (set days and times) and often will recommend a weekly tip. I normally strike up a short-term relationship with the maid (they often come 3x or more a week for several hours a day)...it helps me practice my Spanish. I will usually for their last visit, buy them a nice treat (small cake) and enclose my tip in a pretty card. They appreciate something 'special' and food is always a good gift in a poorer country.
On over-tipping....we will bring Christmas cards with a 100 peso note to our usual haunts the week before Xmas and hand out to the servers, even those not waiting on us that night.
It is easy to be generous in Mexico. Our dinner meals for the two of us with 1 or 2 wines each rarely go north of 400 pesos total. Right now that's a shade over 20 US bucks and includes taxes.
