There are a few known issues with cambelt failure on "wet belt" engines on this model (without seeing the VIN plate we can't tell you if it is a wet belt engine or not) but otherwise reliability is good. The issue is that sometimes the belt fails before Ford's recommended seven-year/144,000 mile replacement. Given the age and mileage of the van you're looking at we'd either insist on a new cambelt before sale or alternatively, if it's a private sale, factor in a cambelt replacement cost of circa £750 into the price you offer for the van. Otherwise the Ford Transit Custom is a great van to drive with plenty of affordable parts and repair options.