Bit of a spoiler if you havn't read Hord of the Dragon Queen, Episode 3....
There are three black dragon eggs in the Dragon Cult caves and the assumption is that the PCs will destroy them. . Granted, the book says they will hatch within days, but the PCs might not know that and start thinking about the possibility of selling them instead.
the immediate commedy of hatching dragon eggs while on horseback could be golden, but what if they take them to one of the cities that are within a weeks travel?
Im not sure how horrified or interested the locals might be
Sounds like a Black Market kinda job. If there's no black market close by, the dragons hatch. Even if they try to establish contact with an interested party, that often takes a while (communication isn't exactly instant, unless they shill out lots of gold for spellcasters to cast "Message" a lot!), so, again, the dragons hatch.
So unless they find the one randomly shady wizard who just happens to be spending the night in jabumble-town, the eggs will likely hatch, regardless of what their plan is. HIlarity ensues ^_^
I'd be worried about the buyer who thinks he can raise his own black dragons, too. Such a person might not have the best intentions to begin with. If he can't keep them under control, there's a few more chromies out to hassle the world. If he can, he's probably also in a position to screw over the party in the transaction, on top of whatever he plans to do with the dragons. Could make for a fun adventure hook, though.
That's not to say a good or neutral buyer would be impossible to find, but if the party does end up selling the eggs (or whelps), it ought to come back and haunt them somehow!
It does say that the eggs must be kept in a specific climate for them to hatch. My group were only able to carry 2 so they cracked one of them open and watched the poor thing die. They managed to get the other two eggs to the first town and kept them hidden. The party worked out a plan to contact a merchant ship captian to sell the eggs. In the end with some good role playing, one egg was cracked open to prove what they were and the merchant bought the other for 2,500gp. If it was a homebrewed game this would for sure come back to them in some way, good or bad. But the influx in cash made no diffrence in the game since magical items are not for sell, and it made for some fun role playing.
K-Ray
One other thing that I had brought up with my group. Any Evil items that they would want to have "destroyed" could be sold at a temple of some "good" god for the same price as selling it on the open market, with the knowledge that the item will be destroyed. Not sure how this will work out in 5E but it worked well in Pathfinder.
K-Ray
Point out to the party Wizard that some of the material components for his spells are ... parts of dead bodies, eww ... and dragons are known to possess inherent magical power. Perhaps he could dip his components in what's left of the egg yolk?
If he goes for the bait, give him "advantage" on his damage rolls, or double-proficiency bonus on that spell's save DC, or something similar.
Enough to make the spells cool and more-powerful, without being auto-win. But not enough to encourage him to seek out dragon nests.
OR ... One of the PH "trinkets" is a vial of dragons' blood. Another is a bit of flesh in pickling juice. Might be worth a few (2d4) GP each.
Dragon baby-back ribs? 
Of course, guess who has just become notorious in certain circles. 
My players kept the dragon eggs so I worked in a plot thread that Leosin’s monk order (in Elturel) would love to hatch the eggs themselves in order to discover if chromatic dragons are evil by nature, or if a nurturing upbringing can make them good.
For the road encounters I’ve created a bandit clan called the “Imbéciles sans frontiers” (fools without boarders). Their plan is to steal the eggs while the party is asleep and raise the dragons as their own.