Beauty says he's seen a lot of trouble with London horses, "[…] and much of it that might have been prevented by a little common sense" (41.1). It's hard for him to watch little ponies that are made to pull heavy loads—one day he sees one that reminds him of Merrylegs being whipped and mistreated.
He notices that butcher's horses are driven particularly fast, and doesn't know why until he waits next to a butcher's shop one day. He watches the butcher berate his young son for driving their horse too hard, but the son tells him he's always told to rush, especially when delivering last-minute orders of fresh meat. "If the gentry would think of what they want, and order their meat the day before, there need not be this blow up!" (41.6), the young boy laments. So he's basically the pizza delivery guy of Victorian London.
Beauty does say that some boys seem to treat their horses kindly, in particular one boy who sells vegetables with an old pony. "The pony followed his master like a dog […] and rattle down the street as merrily as if he had come out of the Queen's stables" (41.9), Beauty says. Jerry calls the boy "Prince Charlie," saying he "[…] would make a king of drivers someday" (41.9).
Beauty also describes an old man with a coal cart who has a very close relationship with his old horse, and Jerry says, "[…] it was a comfort to think how happy an old horse might be in a poor place" (41.10). So basically, money isn't necessarily the key to a horse's happiness.