Had quite a few and never had any issues when returning. But I treated them like a car I owned, so there was never any issues outside the guidelines for them to challenge.
Get the guidelines issues by the lender and the leasing association. It's surprising what they allow without charge and some things are cheaper to take the charge than get fixed.
Some lenders (VWFS for example) publish a table of charges so you can see what the best option is.
One tip - clean it and don't leave it on fumes - let the assessor have some fuel to get back to the depot.
I do remember last year a colleague who I had told of a really good deal handed back a 4 year lease, 2 tyres under legal tread, service light on the dash and filthy. Got hammered for all sorts (after being refused the first collection due to the illegal tyres, which was also charged), all clearly explained in the documents send to him when due to arrange return, and he didn't even check them until he received the invoice!
Has now decided leasing is a ripoff and bought a £20k car from a large car supermarket for £500 a month for 5 years!!