handling
I think they are called handling agents because they handle your money. The Business model is simple. If it normally costs around £15 for a landing fee a handling agent will multiply this by a number usually based on their hat size and then charge you this new number. If you have parked within five yards of the terminal building they will bring a transit van to you and drive you half a mile round the airfield until you are as far away as possible from the taxi rank or train station. Apparently this is to ensure you feel sufficiently handled. On the way you may be exposed to the hangar full of expensive Citation jets which you are contributing to the upkeep of.
This of course is not based on any personal experience and the example above does not refer to any particular handling agent.
I frequently fly a twin which apparently requires more handling than a single and most modest sized airfields now insist on handling for twins. Increasingly this is being extended to singles.
Where you need a service, want transport to the nearest public transport facility, want the weather ready for you for the return trip, and want the aircraft refuelling whilst you are away I have found many handling agents (although not all) to be very good. What I object to is being made to pay for a service i don't want - reminds me of the joke about service at restaurants and the charge the customer wanted to levy for makiong love to his wife - a very 1990s joke so if you haven't heard it I won't repeat it here in case I start to sound like Jim Davidson.