Do you have to leave a tip in Thailand, in restaurants, after a massage, at the hotel, for the taxi?
First of all, it must be said that the French have the reputation of being stingy compared to other tourists, because other nationalities such as the Japanese or some Anglo-Saxons who do not know the customs, are used to leaving too much, in fact they do as in their country.
And often, in countries that are not used to receiving tips, the fact that some customers give them creates an expectation and an increase in prices.
The most important thing is to tip the masseuses who are employed in the salons and often do not earn much.
There the prices for the effort are low and they expect to be tipped.
I have always seen Thai customers leave a 50th of a baht after a Thai massage.
Afterwards, in the tourist areas, there are salons that charge very high prices, where the tip may be included in the price.
In general, tipping depends on the type of venue you are visiting,
In a normal or street restaurant, they do not expect to be tipped, but in "trendy" or luxury restaurants they are.
You can see from the waiters/waitresses, if there are a lot of them, well dressed, they expect to be tipped but it is not compulsory.
You can give some if you have stayed for a long time, ordered a lot and the service was good, between 10 and 50 baht will be enough.
In hotels you can leave a tip for the luggage handler, such as 20 baht or more if he had to carry many bags.
You can leave a tip for the maid, but generally, except in luxury hotels, they don't expect to receive one.
In taxis, they often take it themselves if you don't have the change, you can leave something if the service was really good, but usually this is not done.
For private guides, it is common to charge a larger amount, such as 50 baht for a short tour or 100 baht or more per person for several tours, if he or she has been competent of course.
Tuk tuks are already an expensive form of transport, and if you use one to visit several places, it will have earned its day, so you don't have to tip.
In karaoke bars, if a waitress comes and sits with you to serve and chat, you should leave a tip, from 50 to more depending on the time spent and the friendliness.
In trendy bars and karaoke bars, it is common for customers to leave large tips to seduce the waitress or escort, as a way of signalling that you are interested.
PS: I am putting here mainly the minimum amounts, you are free to be more generous...