I work in a pet shop so this is my experience from that, rather than my private breeding, and naturally it may be different given the countries! About 75% of the rabbits we get in are the rejects from show breeders, so there are a fair few good quality rabbits, but buyers are looking more for 'cuteness' factor so the better standard rabbits aren't the first to go. In terms of breeds we sell plenty of Netherland Dwarves with the smallest rabbits nearly always selling first. For local private breeders the lops are a current fad, again dwarf/mini type, with lion lops and anything 'fluffy' selling for £40-60. In terms of cost we sell ours for £30 and give less than half to the breeders, so usually with expensive breeds the breeders prefer to pay the upkeep and keep for longer than sell for less. Rex types are less common, but when we do get them in they sell pretty well, mainly because they are a 'nice change' from the fluffies - I think if we had too many in a row we may struggle a little more.
We had a litter of Dutch brought in that didn't sell for around 5 months (lovely playful/friendly rabbits), while a good 5-6 litters of Nethies sold in the same time frame, same story with the full sized Blanc de Hotots - just too big and not the most exciting colours. Temperament wise we do work with rabbits as far as possible, and usually stomping and initial fear is sorted before they're sold (often come in with little handling), but it is difficult to judge personality when they often stay for less than a week. The very rare biters get sent back to the breeders. Really in the shop buyers just look for rabbits that aren't too difficult to catch and sit still when picked up.
Colour... solid white and black are not popular, pink eyes are usually the last to sell, blues are 'in' at the moment, as are anything broken and harlequin. Buyers appreciate mixed colour litters so they have more choice and can select a pair that are easy to tell apart.
And finally sex isn't a huge deal either - if people come wanting a pair and we have a pair of bucks and a single doe left, they will take the pair (with appropriate warnings about neutering and possibly splitting them up if they get territorial). Often it's the children that are more determined to have a particular sex than the adults are!
Overall I'd say in general over here they're mainly looking for tiny rabbits with round faces and big eyes, fluffy preferred, mixed colours, that stay still for the brief period they meet the rabbit.