Blimey! I never really thought there could be consequences for the vendor. I guess that it would be pretty hard to prove by The Big Issue against the vendor, although if they employ mystery shoppers the vendor could be caught red handed. Thanks for pointing that out though.
I just prefer to give the vendor the price of a Big Issue to put straight into their pockets.That way they get £3.75 from my £2.50 donation as soon as they sell the next copy!