I know this is rediculous Racer stuff, but here's what I do. On the first call that I see where it's close I see how the other players make the call and react to the call. I can almost tell who's going to be a problem and who isn't. At the first opportunity after that I appeal to the nobler motive of honesty. Something like an out call that is really out I'll say "good call" or if there's one I'm 50/50 on I'll give them the point and let them know it was close.
If it goes south I'll call one of theirs out. If they say anything my answer is "yeah, we have the same umpire".
UBU "Mr. Badger, I belive we've found the grail!" Well maybe it's just a couple of Donnay x-dual Golds with gut hybrids ;-)