Most DEAs / HIs struggle because they can't actyually offer what home sellers and estate agents actually need - i.e. a completed HIP. Most DEAs can only offer the EPC.
This makes it hard to win business. There are companies out there which provide training and access to systems which allow DEAs to compile their own completed hips. Plus some also allow you to offer deferred payments to your customers (and considering that about 50% of those people putting their houses onto the market this is pretty important).
Check out
www.prontohips.co.uk - they seem to offer a pretty comprehensive package, but there are others available.