Those little black dots are mold that will not come out and will continue to spread. We had those show up on a nice saddle and took it into a saddle maker who told us it was not stoppable. They will spread and the only thing you can do is to try to darken the entire saddle. You cannot leave it in an unairconditioned tack room. Send it back.
I sold a saddle recently on eBay. I figured if the buyer had a problem they would contact me and I would deal with it if they did it within one or two days of receiving it. If you wait longer it gets unfair to the seller because maybe the buyer did something to it... Who knows?
I would have taken the saddle back less the shipping because I never believed it would have gone so cheap. It made me sick to sell it at that price.