1) Is the Broker legal to work in Costa Rica? Check brokers ID (cedula) it will say Libre Condicion free of conditions. He or she will be in charge of the company will gladly give you a copy.
2) Check with the Costa Rican Chamber of Real Estate Brokers (CCCBR) and Costa Rica Global Association of REALTORS (CRGAR) and Realtor.com (international). Check online
3) Registered with the tax department? ask for a copy or a factura electronica
4) Get a real estate agent preferably located in the area you are thinking of relocating to. This is quite important since it will help that they know the area well, its pros and cons, the history of properties in the market there, problems, and they can provide background additional info that can be useful.
5) Make sure you get a buyers agent: which means they will not try to push you into buying one of the properties they have listed for their other clients, but instead they will listen to what you are looking for and try to find the property that best suits your needs, Exclusive homes Costa Rica is a perfect example of a buyers agent that will go the extra mile for you.