I haven't tried this myself, but I saw it on the UndeadLabs forum and thought I should share.
"I haven't tried this on all types of materials yet, just construction. First of all find a garage with one construction material, you call a scavenger to pick it up, then pick it up yourself and return it. Here's the exploit, the scavenger will bring one back as well and you'll end up with double."
i tried this once before, although not on purpose, i called in a scavenger but was able to return the stuff i was carrying before he got there so i just picked it up myself and turned it in, however when the scavenger got there and there was nothing for him to get, it actually gave me a message saying he didn't find anything and i lost some trust with that guy and my community morale went down by like 10 points
i never did that again after that, i always make sure i want a scavenger to come before calling and i always l;eave something for them to get after i do, maybe it only works in certain areas?
cause im certain this happened to me with construction materials, as this was at the beginning of the game when you REALLY need construction materials and i had just found a house with like 3 rucksacks of construction mats and i was all happy
"Our glory and our downfall. Embrace the terrible risks of war; drive home the spear." - A Talent For War GT: Trialzero