At one time handling agents used to waive their fees for very small aircraft and hard-up pilots if you spoke to them nicely. Now, head-office intervention seems to have removed that possibility.
Handling agents can do a lot for you and in my experience are very helpful. They will often save you the cost of a taxi by driving you a short distance off the airfield, eg to a station. They can often get hotels at discount rates. They liase with the refuelers, file your flight plans, get you the weather for anywhere and (certainly at Birmingham) provide excellent free tea and coffee.
If you are going into a main airfield, learn your marshalling signals thoroughly and remember that at many large fields you have to call the ground frequency for permission to start engines. With my Jodel, this then entails walking round the front and swinging the prop. Something of a rare sight at Birmingham I understand.
Oh, nearly forgot, the handlers will pull the chocks for you too if you ask.