In Borderlands 4, at the Ruined Sumpland, go and talk to Penelope Streams to accept the Normal side mission “Vend Of The Line“. The side mission will be unlocked after you have completed the Siege and Destroy main mission. The achievement All Things Vend can be unlocked after you accept and track the boss in this crucial mission. Follow a few more steps to satisfy the requirement for unlocking the trophy.
All Things Vend Achievement/Trophy Guide For Borderlands 4?
Accept and track the quest, Vend Of The Line, and defeat the Vend Zane boss at the end of the questline, who is found at Grindstone Of The Worthy. Once you have defeated the boss, there will be a wooden board placed on the ground. Similar to how you have been recovering the clue of the puzzle by entering the correct sequence of the symbols by selling the guns of the same rarity.
On the wooden board, on the ground, there will be symbols marked on it. Therefore, all you need is to sell the gun’s rarity type following the same sequence as the wooden board, i.e.,
Sell Green -> Sell Green -> Sell Green -> Purchase Orange.
Let the dialogues get exhausted completely, in order to interact with the Vending Machine as per the quest to buy Legendary. However, you can do that and get the achievement by simply selling the green rarity guns and then purchasing the orange rarity gun.
The achievement is missable as some might ignore the symbol or code marks on the wooden board, as the quest does not involve it. Now, you know how to get the achievement/trophy All Things Vend.