The most i've ever made is about £30.
Some of my friends have made more than £100.
I only do it once a year when having a clear out and today I actually made a loss as we were rained off...we did get rid of a few bulky items though.
I don't like doing them much but would if I knew how to raise the cash.
Some pile it high, sell it cheap.
If you have made money at a car boot sale...please what is your secret?