Some insurance companies where I live prevent extortion from tow truck companies by including a list of authorized tow companies as a part of the policy. Cars that aren't towed by those companies won't get paid out (or get less paid out, not sure on the details). Perhaps something similar could help here?

Given this situation though, it seems like the tow trucks might just violently threaten someone until they agree to let them tow their car while they wait for an authorized company to arrive. But perhaps that is easier for the police to deal with than organised crime.