You can check an immigration adviser on the Immigration Advice Authority (IAA) register, which replaced the Office of the Immigration Services Commissioner (OISC), and confirm that their organisation and permitted advice level cover your matter. If they describe themselves as a solicitor, check their firm or practising details with the Solicitors Regulation Authority (SRA). Ask for a written fee estimate, details of who will handle your case and information about complaints procedures before instructing them. Authorisation does not guarantee a successful application, so consider obtaining advice from a regulated professional familiar with your circumstances.