Three years ago I did some freelancing for a client. It was one of my first clients when I did the freelance switch.
I did 2 bigger and 2 smaller projects for him and all where catastrophic. He is terrible in project management and getting specs and offers straight and is horrible at communicating with clients. He is really pushy like the world would end if we didn't ship tomorrow, even though all projects where heavily delayed.
All these projects where really, really stressful for me and I only did the follow up projects because I was in the process of buying an appartment and needed the money.
There was never a problem with money, he always paid in time and sometimes he even did compensate for the extra time. I was loyal as well and did some smaller change requests for free.
Now there's a big change in the underlying shop system of that bigger project and he needs my help. I haven't worked with that shop system for a while and it would take significant time for me to get up to speed again. Therefore it's very hard to give an estimate and I already know that estimating for him is very crucial, because things tend to escalate.
Legally, my warranty deed is over.
I have a pretty healthy ecosystem of freelance clients at the moment and am fully booked.
He is bombarding me via mail and skype on if I have time and can help him.
I don't want to do that.
What's a gentle, not offensive way to tell him that I do no longer want to work with him?