The previous owner of our home had this problem. It delayed the house purchase by several months. In the end he had to give the tenants a 6 month deposit (their credit rating was awful) and find a suitable tenancy on their behalf in order to persuade them to leave.
His MIL recently moved in next door to us. She told us how sad it was for him that he'd been taken advantage of and how shocked he had been to find, on their departure, that instead of the single woman he had let to there was a family with 5 kids and several pets who had caused significant damage to the property and stolen fixtures and fittings.
Of course, no sympathy was expressed for the people who had to fix the damage and replace the fixtures and fittings, tear up all the carpets due to being ruined by pet waste, deal with the bailiffs for the previous tenants due to the unpaid debts (he clearly hadn't bothered to run credit checks before letting) and undo the bizarre "decorating" and dodgy that had been done. AKA us.
What fixtures and fittings actually were left in place were of such poor quality that they had to be removed anyway, or have since broken. We are trying to get round to replacing the door handles as nearly all of them have either broken or fallen off. The boiler was so old that they had stopped making the model before the turn of the century.
Break out the tiny violins for the man who did as little as possible, failed to fulfil his legal obligations, never once inspected his own property in all the years they were moving in children, dogs, cats and ferrets, spent the bare minimum required to make the house habitable, and promptly abandoned the whole situation when he realised the house he had sold to us was not the house listed in the deeds or the one we'd been shown around.
The gas certificate was just one example of his incompetence and laziness.