The summary of the sensible answers is 0% neither costs nor earns the dealer anything other than helping him/her shift bikes.
Why then expect a discount?
Not a great summary really.
0% finance always costs the bike shop something – 5-12% dependent on size of shop/turnover through finance etc and the deal they’ve managed to strike with a credit provider.
If you pay hard cash then you save them the 5-12% less any banking fees they may incur.
If you pay card you save them the 5-12% less any card fees they may incur (typically 1-3% depending on card)
So you can argue that, if you turn up with 3.5k in cash you should be able to get some kind of discount assuming you aren’t rubbish at negotiation.
I think 10% would be good going, 5% more likely. Also very dependent on how desperate the LBS is to get 3k in the till. Can swing things massively.