This would depend on what the issue is. For small aesthetic problems (ie. scratches/dents you have not had the opportunity to fix) we would advise you to contact the customer as soon as possible so they are aware that your campervan might not be looking as great as usual.
For bigger things (appliances not working, broken awning, hot water not working etc.) you also need to inform the customer immediately. Depending on the customer, they might be happy to proceed with the booking with something broken, and if that is the case, we would strongly advise offering some form of discount. If you are unsure what to offer, please reach out to the team.
In both cases, what you should not do is wait until the customer arrives to pick up the van to inform them that something is broken/unavailable for their trip, as this leaves the customer with a really negative first impression of your campervan.