I've worked in the hospitality industry for over 40 years in the US, Canada, Europe, Hongkong and Thailand and lived or traveled ( mostly on holidays) to most parts of the world. Tipping in hotels and restaurants is common and expected in most countries either directly by the customer or in a service charge added to the bill. The service industry is very staff heavy in order to provide good service to the customers, so the employers pay lower wages than the staff may deserve ( even if it is the required minimum wage). so employees need their tips in order to live in a reasonale life styly ( I said reasonable not great!!!)
Employers cannot affort to pay higher wages to the large number of staff that are needed to provide the level of service expected by the customers in hotels and restaurants. If they were to do so they would either go bankrupt and out of business or need to substancialy increase prices for rooms and/or meals.
You may have noticed that in recent years more and more restaurants are adding a service charge on to their bills. (Hopefully all giviing it to their staff)
The reason for this is abundantly clear by reading the number of "cheap charlie" posters on this thread who would spend thousands of Baht on gratifying themselves but are to tight fisted to leave what is cosidered minimal 10% tip in a resaurant for the staff who have taken care of them and improved the enjoyment of their meal. Tips in most restaurants go not only to the waite staff but also to the kitchen staff who prepare their food and cean up the mess after they leave.
I agree that in a buffet where you serve and even cook your self, a lesser tip is appropriate but it should still be at least 5%. After all who do you think cooked the food for you or in the case of a self cooking venue, prepared and cleaned the ingredients for you too cook, who is clearing and cleaning your table, bringing drinks etc. and washing the dishes etc. after you leave, are you also doing that yourself?
I'm sure some of the posters will not agree with me but try to put yourselves in the shoes of the staff who take care of you when you eat out,some you se and many you do ot even see throuhtout you meal , but all of whom put in a lot of effort to make our meal and enjoyable one. Even on days when some of you are in a foul mood and take it you on you waiter/waitress, they still have a smile for you and try their best to satisfy you requirements.
Sorry for being so long winded but I thought this needed saying and I hope it will make some of you think twice before being rude to your waiter/waiteress (I've seen it too often over the years in the business) and about leaving a tip. Naturally if the service is bad, by all means leave less or none at all. If the service is exceptional, leave more!!!