I've only ever been scammed once. Unsurprisingly, it was on SR2. I had made a few big orders from this vendor (honestly forget his name) which were successful and had some of the best stealth I've ever seen. He went on vacation mode for a while and then came back with a huge "return sale" that ended up being a big exit scam. I only lost $50 so I counted myself lucky since others had lost upwards of a grand. That was enough to teach me the value of Escrow.
Another time I ordered a gram of PlatinumStandard's Cocaine. Given the guy's amazing feedback and reputation I had no problem shelling out $180 for the gram. It never showed up. I'm pretty sure this was a mistake on my end, since I had it sent to a private mailbox I had bought and might have screwed up the address or number or something. I was pretty shook when it didn't show up, but two weeks went by and nothing ever came. I took that as a sign to not renew my rental and chalk it up as a loss. I had a friend that was gonna split the gram with me and paid for half of it, so I had to spend another $180 for a ball of mediocre street coke that weekend. Sucks to suck, I guess.
Somewhere between 13-20k during the SR1 seizure. It was in the upper tier of that range.
Before that, about $1500 on a dispute on BMR when that was a few months old. Dude provided tracking but I couldn't prove it was the wrong address because PGP encryption. Mods gave me 75% and him 25%. I got nothing and that was the first time I learned a lesson about padded feedback and being careful about whom you choose to conduct business with.