So if you navigate to the Shops bar, then click Flea Market it'll take ya to the expected page. Then if you look to the right (on PC, anyway, and I would guess adequately sized tablets? I don't use LW mobile, so you may have to look further down the page than you expect to see this) you will see a nice box that says Sell and by default it will be showing your currencies, pebbles and what not.
If you click the dropdown that says currencies, you will be able to select whatever other category you desire; every single wolf you own will be shown here whether or not they are actually eligible to be sold, which is a major design flaw that I suppose we will just have to live with until they feel like getting around to fixing it.
Anyway; the sorting algorithm is also terrible and makes finding eligible wolves to sell truly mind-numbing, but it seems like you have a relatively small den at the moment, which will be a major boon to you here! You won't have to sort through much to sell until your den starts getting rather large. From here, you can list them for MS or Pebbles as your heart pleases.
I wouldn't go below 1000 pebbles when selling wolves, as that is what you get for releasing a level 1 wolf. If you list them for lower, people will buy them just to make a minimal profit-- and that will go doubly so once July hits us, as the Goldsea festival will allow players to release wolves for bonus tickets. My dens are currently absolutely packed to the gills with wolves that I am saving to release at this festival, it's a fairly solid supplement to grinding, since your common-breed wolves can come down off of breeding cooldowns so fast and keep churning out puppies for you allll month long.
If you have any other questions, you can also feel free to ping me here or send me a message. It may take me some time to answer, (or if you ping me here, someone else may also be happy to chime in) but I will get back to you when I can.
