Hey, Im a Tamer and playing since march, and used to sell Horses in the past as a main gold making, here are a few tips:
-lvl 125 horses dont sell like you think even if its max lvl, you will make fast gold by selling horses at market value in the city
- some horses sell at higher value in some citys for example:
Steppe will sell for in Meduli 4-5 gold
Fab 4-5 gold
Vadda 3 gold
Batki 7-8 gold
MK 9-10 gold - Omerta makes shur it kill you and your horse outside town
Desert horses even if its a beter horse, it doesnt sell like you think
Mongrol horses sell only in Batki 2-5 gold because in Batki are no Steppe spawn near but when I put for sale 3 horses at a time, they sell in 5 min
For pesonal use, coming from a player that deosnt buy horses ever i consider Steppe trash horses and i dont care if i lose them and if they make it to 125 i just donate to guild or friends, for Desert its the same thing only it hurts if i lose a 125 one, even if i have a 125 ready in every town.
Now how to use horses in diferent activities its a very debatable subject, from experiance I found some sweet spots that work well for me and my play style.
Good luck,