Sell
mode: menu (same as deposit) opens a deposit chest. Place items in the inner grid. Confirm sells. Cancel refunds. ESC/quit refunds unless market.sell.auto_sell_on_close is true. Unpriced stacks bounce back.
mode: inventory sells the whole player inventory instead.

economy.yml market.sell.prices. market.price_source can follow Stonkz. Permission: smply.sell.use.
Auction

auction.yml controls listing fee percent, max listings per player, and duration (Economy default: 3% fee, 6 listings, 24 hours). Needs Vault to check out.
Shop
shop.yml categories.

-1 = unlimited), and optional permission. Needs Vault to buy.
Kits
group: when LuckPerms is installed, otherwise the Bukkit permission. Staff: /smply kit give <player> <kit> bypasses cooldown.

smply.kit.use, plus smply.kit.starter, smply.kit.daily, smply.kit.vip, and similar nodes per kit.