I only give one Collector pig my relics, because I intend to trap him, kill him (he drops all his items given), collect all my relics and give it to another Collector pig.
Turns out Collector pigs have a certain amount of inventory. My pig got maxed out, gave me a 10 piece, dropped a relic because he had no space for it. You could virtually keep getting infinite oincs since you get a relic back, it just takes a lot of relics to fill his inventory up.
GIF attached, he drops the relic, and a 10 piece gets added to my inventory.
Keep giving relics to the same Collector pig, eventually his inventory will fill up, dropping a relic but still paying you for it.