Hobson's Livery Stable
A used-horse exchange. Willie Hobson is a used-horse dealer, with all the connotations of trust and honesty similar occupations draw in across the Multiverse, be it a used-car dealer or an ex-American president on Roundworld, or a used-flying saucer dealer on Proxima Centauri ("Lovely little runner, squire, only fifteen thousand parsecs on the odometer, it'll get you to Earth and back no bother, anal-probing devices don't come as standard but I tell you what I'll do, seeing as it's that Whitley Streiber you're going to probe, I'll throw the full "making Earthlings feel very ill at ease" kit in for another twenty squirdles, can't say fairer than that, this is lasering me own crucial pseudopod off...").
This is a major business in Ankh-Morpork, and Hobson must be a rich man. As the The New Discworld Companion points out, many people in the city want the use of a horse sometimes, but not all the time. People who own horses often have nowhere to park them, so one kind of customer rents an occasional horse, the other rents stable space, and either way Hobson provides a service. In the manner of a Roundworld multi-storey car park, his building provides stabling for horses on several levels.
It is darkly rumoured that Hobson employs an Igor to re-assemble serviceable horses from the functioning and still twitching parts of those who were intimately involved in cart accidents. Normally, a piebald horse has its black and grey colouring distributed a lot more, er, randomly, than that... and it wouldn't have lines of large obtrusive stitches running all the way from the top of its head down its spine to the tail and then up its belly and back to the head...
American president Richard Nixon was once wounded by an opposition campaign that likened his general standards of personal honesty and ethical integrity to those of a used car salesman... as it turned out, the occupational group that ended up with more of a right to feel aggrieved at being compared to a Presidential candidate would have been used-car salesmen...
Hobson's name is probably a reference to Thomas Hobson, who also operated a livery stable, and is famous for the expression "Hobson's choice". Copied from tvtropes: In the late 1500's Thomas Hobson had a business renting out horses. Many of his clients rode the horses too hard, exhausting them. In order to maintain the health of his horses he established a rule that after a horse was returned it would be put in the back of a queue, and only the horse at the front of the queue, being the most well-rested, could be rented out. This gave rise to the phrase "Hobson's choice", meaning no choice at all.