The seller picks a price and then they can go back and reduce the price if its not selling. when you see a slash.
I use Poshmark to buy and I always make an offer and its normally accepted.
If they send you a discount because you hearted the post they will offer a discount and a lower shipping fee. If you make an offer then remember that it will take away the discount shipping fee. It's better to make an offer and pay the regular shipping fee amount I have found.
I just got a notice they raised the shipping fee again to 7.45 and that's high but if your offer comes in low it kind of makes up for it.
I like to bundle with the same seller, you get a discount that way.
I am very pleased with PM and have bought nice new items for not much money!