Is it permissible to accept a certificate and compensation from a training company that I do not intend to work for?

If the trainee has the choice between working or not, and the training contract does not stipulate that he must work with the company, then there is no harm in limiting oneself to the training and taking the stipend. The decisive factor is the conditions of the contract, based on Allah's saying: "O you who have believed, fulfill [all] contracts," and the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions."