Being very experienced PoE trader throughout several years (and more importantly PLAYER), and being PoE trader (mainly seller) on PA for over a year now all i can say is that temporary leagues have WAY BETTER sell rate than permanent leagues (standard/hardcore). One thing that need to be added to PoE section are remaining type of currency that are not currently included: Vaal Orb, Armourer's Scrap, Blacksmith's Whetstones, Glasblower's Bauble. I sold all of them using different methods but for buyers to find them more easily adding them to Orb subcategory is mandatory (especially Vaal orb). Also when new tempo leagues open u might want to add those 2 leagues ASAP, if possible day before its release since their market are fresh one (meaning everyone starts from scratch) so prices are super high (1 exa sells for 20-40$ in day 1!). On day 2 that price is roughly halved already. And u might (probably need) want to add 1 month leagues as well (maybe even 1 week leagues) for the same reason, people will rush to buy overpriced orbs just to be on the top spot on the leaderboard. I'm trying to think like a player and that seems pretty reasonable from the player perspective.
One more thing, i'm not very impressed how creating new sell offer has been implemented, but over time i got used to it and it's fine to me, but others might not like it. One important thing is that some orders are buggy right from the start. For example i got multiple messages for broken/buggy orders for chromatics/alteration orbs when creating orders for them of Item Per Unit 1, but when i edit it to be 100 per unit that seemed fine. I also contacted support regarding this bug several times but it still seems broken.
I guess that's it for now, when i remember more stuff i'll post.