The clip below shows some clear communication signals in dogs and we can observe them in many situations when dogs are touched. It is interesting and indicates the subtleties of canine communication.
While this is helpful, there are some dogs who would accept touch not because they like it but because they may be insecure and perhaps any contact is better than the worry of what might happen if they are not touched. And there may be a whole host of other reasons why a dog may endure being touched and not actually be that comfortable with it.
Some dogs seem okay but are actually in a freeze, momentarily, before biting. Some roll over onto their backs and this could well be another signal that they do not like being touched. So, as you can see there are many other things to be considered. The more you understand their body language and signals, the more communication you will notice.
By the way – training session = food, so that is why some dogs put up with things, including training.