What is a "duff deal"?

[Gillnetter]

While reviewing some text I read the following and am unsure of the meaning. Would someone interpret this for me?

"You can get a duff deal but not as good as on the high street".

I assume that a "duff deal" is a good thing but I am clueless as to the meaning of "on the high street".

Thanks for your time and consideration.

[Rover_KE]

Sorry - I don't get it, either, Gill.

'Duff' to me means worthless.

'The high street' over here is what you call 'main street' or 'downtown.'

Rover

[Tdol]

For me, a duff deal is a bad or worthless deal or one where you get cheated/ripped off, etc. It could be sarcastic and suggesting that the high street (mainstream shopping) offers duff deals that are in some way better. For instance, the high street and market might both rip you off, but the high street would offer some guarantees about replacing goods, etc. It's far from clear, though- I suppose it could also mean that the high street offers even worse deals.