We would recommend a complete change of locks to avoid unpleasant situations in the future. First of all, the locks may be old and will not last you long. Secondly, you never know who might have the keys to your property. Even if the old owner assured you that all the keys were given to you, you cannot have a 100% guarantee. Third, it's your own peace and relaxation. You can replace the old locks with electronic locks, which will provide you with complete security and peace of mind.