At Bikechain every bike that we sell comes with lights and the required by Ontario law reflective tape on the front fork/rear chainstays. It's more to do with making sure people are safe than anything to do with some sort of liability, there is no requirement in Ontario that bikes sold have to come with any sort of reflectors/lights just that the bikes on the road have to have them.
I would check with the relevant laws in your area as to what is required on a bike being sold. The other consideration is that lights/reflective tape add to the price of the bike so just be aware of that.
As for just bikes coming in to be worked on, I've never heard of a shop requiring bikes to have all of the legally required reflectors/lights to be repaired. Either at a bike co-op or a regular bike shop.