I rarely haggle, but on my next purchase I will. And I will buy a demo otherwise wait for a used bike on PinkBike. I don’t like eBay because they take so much money from the seller. I sold 2 bikes on eBay last year and got absolutely CREAMED on commissions. I’m doing demo-rides for my LBS and taking groups out for them since I know all the trails in our area so well. So I’m sure I’ll get a good deal on a demo bike.
As for everything else, I don’t ask for discounts. Especially not service and I tip big, always at least S10 and up to $40. I have a good relationship with all the mechanics and because of that, my bikes get fixed (unless parts need to be ordered) while I wait. I’m never pushy with them and I think that’s why they offer to work on it on the spot, unless they are super busy which is totally cool.