In the Horse market (or shop as the window states) you can buy horses for gold and/or competition horseshoes.

You need to have trained a horse to level 40 for the horse market to unlock.

The horses in the shop are mostly low level. Now and then you will be offered higher leveled horses but that will depend on the level of your highest horse in the stable.

▲This is the result so far of buying horses from the Horse shop and breeding them along the way. This Goldy was a new foal from level 50 parents. Each set of parents were bought from the market with competition horseshoes.

The horses you can buy usually have better breeding qualities and effects than a horse that you breed or train. Like everything else you will have to pay gold for a really good horse although the selected horse in the image is not bad. The only downfall is you will have to train it up to level 35 before breeding to get the extra breeding effect slot.

Larino: "Whether it's worth it or not to buy a horse is the question. They are pretty expensive and they do not have such amazing traits that you gain a huge advantage. I personally still think buying a horse in the stable for 10 golden horseshoes and training and breeding it as explained in the Horsebreeding 101 article is the best way to go." 

I do not have any comment on that at this time. Once I get this Goldy level 70 to breed with my main I plan to test out Larino's Horsebreeding 101 and I'll keep you informed.

What's new 2020?
You will be offered a new selection of horses every 24 hours. Since the revision of the horse ranch, you are now offered 6 horses to choose from instead of the 3 horses.