First thing's first. Before you hire a builder, you have to make sure that you are aware what kind of work you need done. If you are unable to create a drawing of what you need done, you can always cut out pictures from magazines that reflect what you need to be done in your home. Keep in mind that doing so would make sure that you and the builder are on the same page.
In order to be sure that you getting the better end of the bargain, it would be a good move to ask for at least three quotes from three different builders. That way, you can easily check which builder is the right one not only for your need but also for your budget. Of course, you have to make sure that what you have is a quote and not just a general estimate. Estimates tend to provide you only with a rough pricing which could eventually change as the project progresses. Make sure that the builder is able to provide the quote for free as there are some builders who would charge for the said service.
Just like with anything else, you also have to check how long the builder has been in the industry. While it is not a solid basis for the quality of work, it would at least give you an idea whether they are able to provide satisfactory service. After all, it is kind of hard to stay in a competitive niche if you are not able to provide at least satisfactory work. While you're at it, it would also be a good idea to check if the builder has the right licenses and certification. This would also be a good time to see if they have a builders insurance in place. A builders insurance is a kind of property insurance that most builders have in order to protect them from indemnity arising from building damages. In most cases, builders also have a worker's compensation in place in order to protect their employees should they become injured in the line of work. Now, in the off chance that you think the coverage being offered by the builders insurance is not enough, you can always get in touch with insurance brokers so that they can work out a coverage that would supplement what the builder already has in place.