The problem with a driver letting someone ride for nowt is that the lucky beneficiary is just as likely to post the fact here as did the aggrieved OP with the opposite experience, not good for future employment prospects if the individual is identifiable.
An earlier poster mentioned the erstwhile NX 383 service (Edinburgh - Wrexham via Carter Bar). I took it a few times between Edinburgh and Manchester, having all day at my disposal, because it was a nice scenic route and, though longer in distance, was considerably cheaper than the normal route vis Glasgow.