The handling fee is always the same, regardless of the actual customs cost. I think my last DHL one was about £20, of which £15 was their handling fee. I don't mind the fees, but some of them in no way reflect the true cost of the involved processing.

I've noticed customs getting a bit more thorough in their checks, as I had a couple parcels opened and resealed by customs last year, which I'd never seen before.
And I'm aware of somebody who got a revised customs bill for a shipment for the full RRP of an item, despite the fact he got it at a discount, however the CN22 (customs declaration) was for an even lower value. He never appealed it, as it would cost him more in time and effort for all the money he'd of gotten back.

It just shows customs are using their brains a bit more. Pick some random parcels, find out what's in them, google the contents, and see if the stated value is realistic. They won't impound any parcels, unless there's something illegal in them (i.e. counterfeit goods), just revise the customs charges.