Originally Posted by
Bakpapier
I think most long distance bus companies still allow on-board ticketing. At least Flixbus does, looking at their website, which is a major bus company in Europe. It's of course different if a company wouldn't allow it.
While I don't know this for a fact, I'm willing to bet that Megabus and Greyhound will NOT sell you a ticket on the bus (and I'm not a betting man).
Originally Posted by
Bakpapier
Ergo: you will never be able to see if there were free spaces or not if you never fly.
Au contraire,
Flight status and information page at United.com will give EXCELLENT info of just which seat is available about an hour or two before departure (not as accurate before that). And even better AFTER departure for about 24 hours. Don't fly AA enough to know how accurate their seatmap is, and don't fly Delta at all.
Decided to Google, and I can confirm you CANNOT buy Megabus tickets on the bus.