As a scam investigator, here are my thoughts:
Scenario 1I will give each user 0.1 BTC, up to a maximum of 100 BTC.
After paying out 50
BTC:
Sorry, I ran out of BTC. I know I said 100 BTC maximum, but please respect my situation here.
This one needs more information. If the BTC were being given away while nothing was received in return, this would not be considered a scam. If it required someone to do something, it would be a scam. For example: "Everyone who signs up at my affiliate link will receive 0.1
BTC, up to 1000 users!"
Of course, they can still close the offer early, but they would still be responsible for everything prior to that (maybe with a few minute leeway right before they closed the offer, though)
Scenario 2Send me 0.1 BTC, and I will double it in a week! I will double 100 users!
After doubling 50 users, refuses to double 51
st user, paying it back in a week:
Sorry bro, ran out, and I need to minimize my losses. I paid you back your 0.1 BTC, sorry it took so long. I don't know what I was thinking when I made the OP.
This is a scam. Imagine this simpler scenario:
I take out 2 loans: one from Hashking, and one from Kluge. Both loans are for 100
BTC and have 10% interest for a one-week term.
I pay back Kluge 110
BTC after the week, but I only pay Hashking 100
BTC.
If I'm unable/unwilling to work something out in good faith with Hashking AND nobody else is willing to loan me the 10 BTC difference AND several days have passed without any kind of resolution, I deserve the scammer tag.
Scenario 3I'm going to bet up to 100 BTC that the Penguins will win the Stanley Cup this year. Just send to [address] and I will return to one of the inputs if I lose. 1:1 odds, normal rules apply. I'm well trusted here, so don't worry about escrow.
After the Rangers win the cup:
I'm so sorry! I intended the bet to be a joke. I never expected anyone to send. I returned all the money sent, plus 1% extra as compensation for the time.
Unless you can prove that you wouldn't have been paid if the outcome had gone the other way, you're a scammer. Even that would be shaky, though.
Scenario 4I'm going to bet up to 100 BTC that the Blue Jays will lose tomorrow’s game. Anyone interested, post your address and amount here!
After the Blue Jays win:
Look, I'm not going to lose this bet on poor umpires. It was clear that the umpires were biased, deliberately calling a few shady Jays runs "safe". I'm not going to ask you to remit the funds, but I won't pay out either.
Umpires are part of the game and should have been considered when the bet was initially made. If you try to claim otherwise, I'd ask you to explain why sports that can clearly afford it aren't completely refereed by computers.