My biggest "scam" was probably in High School. About 5 years ago, me and my friend shared this account that I pretty much raised myself, but he paid for membership for me on my other account to train it. I ended up changing the password and selling it to another friend from RS for like 100m because it was almost maxed at the time, and then my friend ended up recovering it although he didn't really play. Other than that I've done small scams over the years for amounts of 30k up to about 2mil. The guy I shared the account with ended up pulling off a 600m scam because we were ranked in Tehnoobshow's clan chat, so it was easier to be trusted by all the wannabes in there lmao.
They made a video about it, but I can't seem to find it at the moment If I find it, I'll post it on here :P