I sometimes draft strangers but only after assessing their riding abilities and, approaching from the side, requesting permission. When people approach me this way I respond favorably. I don’t respond well to people drafting without asking and especially without letting me know they’re back there.
When I don’t want to be drafted, which is most of the time, as I approach a rider going close to my speed I slow down for maybe 30 seconds to rest up – not drafting but as I close the distance – and then accelerate past. This tends to discourage people from hopping on.