Celtic have a gambling and beer sponsor on their shirts (Dafabet front, Magners back). Get Wonga on their shorts and they've completed the unholy trinity.Should follow suit in what Celtic do, offer both a sponsor and none sponsor version of the shirt.
Appeals to all - those who want the full replica version and those who don't want to be associated with gambling but still want a shirt and those who just want a clean Blue top with a badge and Umbro logo.
Gambling and alcohol are part of sport though so what are you going to do? No alcohol allowed in the stadium? Not allowed to put bets on the match? Payday loans I would draw a line at as they have no link to watching sport and they are horrible, bloodsucking companies.