Hello I need help how much do you sell a pet for without going over what another player is willing to spend thanks for the help

Depends on the pet in question. There's all sorts of factors like:

Species, if the pet is themed Tagged or Purebred- if it is, what theme-, traits and TP, colours if not a theme, stats, regen, if the pet's been mutated or not, if the pet's been bred or not, if it's a project pet...

Best way to figure out price is to look in the Advanced Search for similar pets.

Species; some species are more popular than others- although with any species you can potentially find the Enthusiasts who just like giving a home to pets of that species

themed Tagged or Purebred- if it is, what theme; some themes are rarer than others

traits; newer traits, and more recessive traits in general, are more likely to go for a higher price

TP; more traits typically gets a higher price, though it depends on what they are

colours if not a theme; if a pet just has a bad colour palette, it's not likely to sell for much based on it

stats; higher stats can fetch higher prices

regen; pets that are regennable can fetch pretty decent prices

if the pet's been mutated; people like to have the chance to choose to mutate a pet if it's a Tamed pet

if the pet's been bred; breeding a pet means a person can't do things like gender change.

project; whether it's a Max stat project, a PureBreed project, or a personal design project, these tend to get higher prices