Well I've worked as a waiter before and I would certainly never expect to be tipped for the kind of service I get here.
I tipped anyway for the first few years I lived here and generally found that as a result I got worse service, not better service. I guess people thought I was their "friend" now since I gave away free money and would be willing to wait even longer for things, and "understand" if nobody bothered to get the order right.
Of course in tourist areas things are very different but I am talking about the rest of the DR where staff and customers are primarily Dominican.
I've run bars and restaurants here, and I happen to know that even though it says "ley" (law) on the receipt, it is referred to by waitstaff and management as "propinas" (tips) and is supposed to be devided up among the service staff. I've also noticed that Dominicans almost NEVER tip above the "LEY" unless they are planning to try to date the waitress. Unlike the US where waitstaff can be paid half of the minimum wage (except in California) and depend on tips for the other half, waitstaff here do make at least the minimum wage, and in many cases more.
I am firmly of the opinion that this is a perfect example of how well-meaning socialistic systems actually turn out to be bad for everybody.
If you have a restaurant you should know all about double accounting and how most restaurant owners only devide up about 30% of the money they take in as "ley" among the employees and keep the rest. If they devided it all up, it would be harder to hide the fact that they report less than half of their sales to the government so they don't get taxed for it.
The customer has no way to passively express a lack of satisfaction, since the law requires him to tip at least 10%, and the individual employees have no motivation to work well and pleae the customers, since the tips get devided up between everybody, often with lazy managers taking the lion's share off of the top and the janitors and dishwashers being awarded a share of the little that's left, along with the waiters who get so little of tips that were meant for them that they see no connection between good service and money.
Also employees have no motivation or tendency to rise in an establishment, the classic model where a young person would start out washing dishes and then move up to busboy, waiter, and finally manager simply does not happen.