Ah, upon research I see that the so-called "Greyhound Express" routes are not overbooked and are therefore acceptable. The others are overbooked.
Luckily some of the Atlanta-Savannah trips are "Greyhound Express". This also makes it safer to get a non-refundable fare, which it totally is not safe to do otherwise. If you take Greyhound, I would advise *only* taking the "Greyhound Express" reservations.
Actually, the non-Express routes have showed up as "SOLD OUT" recently, so Greyhound
doesn't overbook anymore. This can be proven on my New Year's trip to San Francisco, when the D4505 was filled out to every seat, yet no one was left behind.
The problem is that Greyhound doesn't always fix bus models to routes, and different bus models have slightly different capacity, so slight overbooking is hard to avoid. But again, the D4505 has the lowest capacity, at 50 passengers, and that one was
perfectly topped out, NOT on an official Express run, though the schedule was actually structured as an express (few stops).
BTW, back a few months ago when they still overbooked, that wasn't because they did it on purpose, it was just that they had a mess of too many different bus models and their Trips computer was overloaded and outdated.
Now that I check again, Greyhound may have rebuilt 502-505 which were the old buses on Atlanta-Savannah before the D4505's came. After rebuilding, they have one extra seat compared to the new buses, so that won't hurt. Besides, the rebuilt oldies are a lot more comfortable than the new ones. That's the one on my avatar.