Ok, so I try to increase my supporter count b playing practice games, but the teams that appear in my area are all significantly higher in * rating than me. Not a bit, by a good 10* average.

I'm level 20 and 84* my suggested opponents all higher than me (when there are teams there as sometimes it takes days to increase from one or two teams.
I spent a day playing lower ranked teams to get training points and increase spectator count only for the slots to remain empty for days, then refilled by much higher ranked teams...

Now I know that other teams get lower rated teams beacuse several times a day I find that I've been chosen for practice matches by teams with 10* and 20* average higher ratings and a few league rankings higher, get beaten, lose all the fans I've been working hard to increase.

Now I can handle being a whipping boy now and again if I thought I could do the same to recoup my fan losses, but it really doesn't seem to be the case. How does that work then?

Teams are matched by number of fans rather than strength of players. Do you have a level 20 or 21 stadium?

You need to get smart with who you bring in, in transfers. I suggest you spend 20 mins or so going through every position putting a bid of 1 on every player with a higher skill level than your current players. I suspect you will be pleasantly surprised what you get. I just restarted my seconds from almost nothing at level 24 (all there was 7* players) and I managed to pick up 20 100* (and slightly +) for 20 coins in total...