GEM, I've understood how it works mate. Did it myself when I was a new WC. But eventually, you get so much work that these mongs who clean for a few quid don't matter anymore and you don't need to work 15 minutes for free becaus you have more work than you can handle. Even more work starts coming at you when you get well known, so you haven't got time or interest to work ANYWHERE for any amount of minutes for ANYONE for free.
You're not there yet, judging by your complaint, but believe me. If you put enough custies in, you will get there.