Hello there!
Ive only been here a couple weeks but am now at the point where I would like to sell some of my Sylestis to make room for new ones in my stable and to get a little gold if I can!

Is there a guideline somewhere on pricing? Ive noticed a large difference in pricing seemingly dependent on the genetics and mutations. I want to sell some Sylestis; but dont want to over-charge or let something valuable go for too little. Thanks so much for your time and to anyone who can help!

Selling sylestis can be very hard sometimes, and there isn't a guide for it as far as I'm aware.

Advanced search can act as a decent guide when you have something specific you're trying to sell. I'd recomend matching as many of the filters as you can before the trait filter, since searching for things with M1 and M2 visible often hides comparable pets with G3 and M3 visible - if they're both 2 visible traits they're probably comparable.

This probably doesn't help with the pets you have, but might be interesting: pricing projects has a few very different philosophies kind of like pricing paintings. Some people like to base their prices on the resources that went into the project, like essence, dyes, stat philters, or time. Others come up with a formula of price per visible trait, which you just set so that it feels right personally and/or in comparison to how others price their projects. And still others just set a price independently for each project, based on what they think it's worth or what they think will sell.

I would overall say that selling is really about getting the right person to see it at a price they think is reasonable, and that can take a long time. For me, if I sell tagged themes I price based on advanced search and leave up indefinitley in case someone decides to search for it. When selling pets I've bred it's almost exclusively offspring from finish projects, which I sell to order when I'm bothered to upkeep a thread with images of the breeding pairs, or allocate a couple of stable tabs to keeping a mix of ones I know have sold in the past just in case someone decided to look what I have for sale. Non-themed pets I've captured, which I generally don't think are worth much, I leave up for sale for a week before cutting the price to something very low, and release them if that doesn't work after another week.

Sometimes people will buy anything at very low prices specifically to release them (usually under 100, but I've seen it go up to around 500), because occasionally events have incentives for releasing, and there's always a minor benefit to finding themes in the late game Lost Grove if you release pets over 42 days old. But at that point, the eventual sale probably won't even cover the feeding costs.

I hope something in there helps

Silverkitsu summed it up pretty well, pricing is always hard. Definitely browse Advanced Search a bit! I might start with searching by species, looking at the kinds of pets that were listed for sale recently, thinking about the number of traits as well as the colors.

You could also make a thread in the pet sales forum and ask for offers on the pets you're trying to sell :)

Thank you so much!

Thank you so much as well!