I guess it depends on what you are looking for. I try hard to vary it. I post sheets with a variety of species like these two. I'm always happy to adjust poses from canine to feline or feline to canine, or even equine to canine or a snake to be a dragon. I'm happy to add wings to things.
I'm quite flexible with my YCH. Though I know a lot of people aren't, and that's because they'd have to take time to redo the sketch. A lot of people don't want to because that is extra time/money they lose "fixing things". I'm happy to do so, but if I think it'll cost me a lot of extra time, I'll ask a little extra, which is very rare.
Idk how long you've been watching me, but please know all of my YCH are very flexible. I'll always write on the YCH page/deviation what I'm willing to change it to. I've even considered just making backgrounds and having people take it and give me a character to put in there so there will be no sketch to redo. u_u though I don't know how I feel trying something like that.
YCH stands for "Your Character Here". Basically I make a sketch with a creature in some sort of pose, sometimes with a background and someone buys or bids to have the artwork completed with their character.