Sneaking onto TER really depends on the line, or the region you're in. Some regions are very chill, some others deploy controllers in every single train. It's pretty much a toss-up ! The longer the ride, the higher the risk of getting caught, and the controllers know all the tricks (the toilets, hiding on the luggage rack...). To be precise: it's hard to know if the line you're on deploys controllers regularly, but if they do, consider yourself toast.
My advice is to sit in the middle of the train: controllers come from the locomotives at either end and work their way to the middle, so you'll have time to see them coming and advise from there.
Some work-arounds if the controllers are going towards you and you can't escape them:
- buy a ticket for the next train on the SNCFCONNECT app. (sometimes controllers won't check the hour at which the ticket was bought and you can get out of a fine).
- tell them you didn't have time to buy a ticket / couldn't find the tills, and ask to buy the ticket on the train (but then it'll be more expensive than in the train station).
If you do get caught and they don't believe your crap, the fine is 50€ for journeys under 100km. they fine you and then throw you out at the next station.
Good luck !
