There's also a @sourovafrin's market bot in the Cheap Monsters Discord channel. It gives a 3% cashback. https://discord.gg/KWkY6Nf
And MonsterMarket gives 3% cashback on cards, and 2% on packs - just checked this morning with @reazuliqbal
I knew there was others and cheap monsters was on the tip of my tongue when creating this topic. I'm happy someone stopped by and mentioned them. I'm less familiar with CheapMonsters so I couldn't say much on their services provided (although I'm sure its top notch). There's other as well but I'm unfamiliar with them.
(Monster Market) 3% on purchases / 2% on pack purchases is displayed on their site. Thanks for mentioning that, I have edited the topic to more correctly display the information.