I typically find the more colorful/more genes a wild horse has makes it more valuable. This also counts for dapples, skews (like the one you have), and variations which don't display on the gene layout. 

Additionally, the horse's breed also plays a factor in how much it will go for. I have noticed Lusitanos are hot right now (regardless of how colorful) because it a newly released breed. However, other horses like Welsh Cobs, Paso Finos, etc., don't always sell the best because they aren't super popular. You can still sell them, you just might not get as much as say, the Lusitano. 

Thankfully, Irish Cobs are pretty popular! 

That being said, wilds vary heavily in price and depend largely on how much folks are willing to pay for them. The best rule of thumb is… Is it colorful/have a lot of genes? Then yes, it will sell. If it is just a plain bay, it will still sell, just for not as much. 

An example of how much folks are willing to pay….

https://horsefable.com/horse/2062811 I bought this cutie for $100,000 because I NEEDED her. She is dapple + Skew and I couldn't resist :P