1) After sending goods for later payment, perhaps such as used motorcycle tyres (otherwise known as 'part worns) You would say to the receiver:
"you better not gubbs me, I need the
money for my poor old sick and dying Granny"
2) If you were out of luck, or just a tight
bastard, you could actively try to obtain goods for
free. Such as part worn motorcycle tyres. In this instance you would say
"Oi Kev, fancy going out and doing a bit of Gubbing"