Availability of a van with a tailgate is another problem as there aren't many company's who order this option - apart from the RAC and AA.
Barn rear doors are the option of choice as they can load pallets of stuff with a forklift. You can't do that with a tailgate.
At one time, the resale value of a van with a tailgate was less than the same van with barn doors. But as there aren't many vans with tailgates, this is difficult to quantify.
There is a good market for ex RAC and AA vans as they are supposed to have an excellent service and maintenance record. They seem to hold a good resale value, even with some having really high mileages. Personally, the colours would put me off, especially the RAC ones.