To get back to the original question of whether you would report a fare dodger, I once did. I'm going back 30 odd years but I was in the ticket queue at Newport one Friday evening when the guy in front of me asked for a single to Abergavenny.
Upon being told it was £1.80 he exclaimed "HOW MUCH??" and stomped away from the counter without buying the ticket. IIRC that was nearly twice as much as the then bus fare but a day return was only 10p or 20p more, and given it was more than twice as fast as the bus a return was more than competitive (it's now £8.50 single, £10 day return).
Trouble was, the last bus had gone (even in those days it was at about 18.30) and the train was now his only option unless he wanted to get a bus to Pontypool and walk the remaining 9 miles or wait until the next morning. I watched the guy walk to the station exit, hang around for a few seconds and then walk back in, buy a platform ticket and use that to get through what was then a manned barrier.
I was incensed, mainly because I was struggling financially at the time and my train fare was an unwelcome and unexpected hole in my finances. I was newly married but no sooner had we set up in our first home when out of the blue my employer closed the local office and the staff that weren't made redundant were transferred to the Newport branch. Neither of us were earning much, we didn't have a car, couldn't afford to move and even if we had that would have meant my wife either having to reverse commute or get a new job so I had to bite the bullet and travel. Those of you who commute long distances will probably think "oh you poor thing" but we were living over a mile from the station, there was no bus and in those days Abergavenny only got seven trains to Newport on a weekday and eight back. Worst of all we were expected to adhere to a strict 9.00 - 5.30 day (no flexible or family friendly working in those days!), the only train that would get me in before 9.00am arrived at 8.17 (the next got in at 9.03

) and it was the same coming home with the frustration most nights of seeing the 17.35 pull out just as I came tearing up the station approach meaning that I had to wait until 19.00 for the next one, and without having the spare cash to while away almost an hour and a half in the nearest pub (and no mobiles, internet or on-line entertainment in those days either, just a little transistor radio and earpiece!!).
This guy, on the other hand, was smartly dressed with a briefcase, late 30s/early 40s, and when he got his wallet out to get change from the change pouch I could see that he had at least £15-£20 in notes in there as well as a credit card (hey, that was a lot of money in those days - think 60p a pint for beer and scale up from there!), so it wasn't that he had no money or was stranded, he just didn't want to pay it, whereas the £40-£50 a month I was shelling out on train fares, whilst not crippling us, meant cutting back on nearly all our leisure spending and the other things that couples in their mid-20s like to do, so it was fair to say that I was furious.
When I went through the barrier I told the ticket collector what I'd seen, described the bloke and asked if he could ensure that the tickets were checked on the train before Abergavenny. "No problem, thanks for that". I wandered off to the platform and looking back I could see that he was on the phone to somebody.
I couldn't see the guy on the platform but in those days it was mainly class 25 or 31 engines and the old Mk I compartment coaches on that route and guess who got into my compartment and sat opposite me?
We were less than a mile from Abergavenny when the door slid open and I heard "tickets please". I noticed that there was not one but two guards in the corridor as the bloke went through the pantomime of looking through his wallet and turning his pockets out trying to find the non-existent ticket.
"Oh, I can't find my ticket..." I was frantically trying to decide whether I should say anything when the guard said in a firm voice "are you travelling to Abergavenny, Sir?" ("yes") "well I think we'd better sort this out when we get to Abergavenny".
When I got off I could see that he was having a very nervous and animated conversation with the guard who had got off the train and they were joined on the platform by a guy in a suit (from his appearance probably more BR managerial than BTP).
Sadly, I didn't see the final outcome as my wife used to meet me at the station on a Friday evening and we'd get our weekly treat of a takeaway and a bottle of wine on the way home and she wasn't in the mood to listen to my protestations as she dragged me away!
If the guy had been stranded without means of payment or appeared down on his luck I probably wouldn't have said or done anything, but as I said he had the means to pay but just chose not to. Having said that, I suppose theft is theft no matter what the circumstances......