There is no question that there are many competent dentists in Los Algodones. It is also possible there are many more that may not be as good, same as anywhere. The clinic I decided on, Sani, is highly recommended and a couple of acquaintances have used them and been happy. Do your own research, talk to people who have had work done and decide where you will go. Do not be swayed by the hawkers lining the street at the border who promise the world if you will just go to "their" dentist. The fact of the matter is, they get paid for bringing people in.
Print out directions, maps and the address but if you do not know how to get to the dentist you have chosen or become confused, pick out the least aggressive hawker and pay him ($5?) to walk you to your dentist. The chaos at the border crossing can be intimidating to the uninitiated but the savings will make it well worth your while!