If you want to mine bitcoin then you should buy a bitcoin ASIC miner and run it yourself. Do the necessary research first.
Almost all cloud mining services are scams. But there have been a (very) few that were not - although they were not profitable for customers.
So there are two possibilities:
You pay someone 1.0 BTC and they run off with your bitcoin. ...
What you describe happens normally and is not an issue in practice.
Even if one eventually wins out wouldn't a lot of people lose money because of how many transactions were invalidated?
No, those transactions are included in later blocks. I'm not sure of the exact method but I think it must be either that nodes return transactions from stale blocks to ...
(target + space - guess) * 100 / space
So for example, if your numbers had to be less than 200 and you needed to be less than 20 but got 30, your guess is (20+200-30)*100/200 or 95% right.
This makes sense. There were 200 possible results. You needed to be in a range that covered 10% of that space. You missed by 10, which is 5% of the space. So you were 95% ...