Evaluating a New Employee's Background
Since how long was he with his previous employer? Check the credentials with the previous employer. Has he had his resignation accepted? Has he given a proper handover? Has he cleared the No Due? Ask a few questions as to why the previous employer is not giving him the relieving letter and the reason behind it. Check whether the employee has absconded, and if the answer is affirmative, then find out the reason behind it. You can have a rough idea of the candidate.
Ms. Nisha has rightly said that initially, the candidate will be on a probation period, so accordingly, you can mention the clause of termination during the probationary period.
Last but not least, if everything is on the right path, get a declaration from the candidate that the present employer can terminate his employment if, in the future, whatever information he has provided is found to be false or if there are any proceedings from the previous employer. This is for your safer side.