I'm someone who always has a lot of projects going - inventions, car resto-mods, home repair, programming, etc. Inevitably a proportion of the people I meet see this as an opportunity to get someone to implement their Big Idea for them.
There are a few people I trust to do projects for; the projects are limited in scope and we usually trade for time or if it's for a good cause. The ones that scare me are the completely open-ended projects ("revolutionize an industry", "million dollar idea"), or when they say "wow I might have regular work to send your way." (I already have a full-time engineering job.)
The problem is my personal time is my most limited resource. If I had additional time I'd use it to further one of my own backlogged projects. When I carve time out to be social, getting roped into another project as a result of that does not help me keep a balanced life.
I'm happy to teach, but few want to learn. I can critique an idea and advise how to fix it, but have learned the former is never welcome and the latter is never heeded.
Yet I'm still trying to be social. How do I tell someone, "I don't have time to do things for you," without coming across as saying, "I don't have time for you"?