If Bitcoin is not being fight against in your region and there are more people that knows about Bitcoin in your region, you will surely have rich guy customers that will pay with
Bitcoin to get their car fixed. Customers love to get discount and from the discount you have agreed to offer the people that will pay in Bitcoin, you will surely have them coming. Some people that are not even familiar with Bitcoin will buy Bitcoin so that they can pay you with it for the sake of the 5% discount. Keep it up @OP, kudos.
Rich guys coming to your shop or rather OP's shop isn't a guarantee just because he's offering a 5% discount on repair if they pay in bitcoin, that's not how it works in this kind of setting. The people that would be talking about bitcoin with OP and will inquire about it will definitely be a thing in this situation and I think that's the best one for the whole community in my opinion, look at it this way, the more people are talking about bitcoin because of OP's innovation in his payment model, then there's more people that have the potential to invest in bitcoin, then the more we would see contributions of OP for the increase of demand in bitcoin.