new player trying to understand trading

i try to use elve and gg but sometimes they don't have items or the toys and such and so i feel i've been overpaying in some trades...im also having a hard time building up my inv of better pets. i'm new and just don't entirely know what im doing with values and such 😅 is there like a quick way to kind of learn the values and remember the pets in which categories ? there's so much and ik the values are all over. one common can be a lot better than another. i feel i've been making bad trades and i rlly want to do well in this game cause i like it :(