Im try to understand verifing bitcoin transaction but I cant find this part anywhere. Summary, the proces before forming blocks. My questions is:
1) when i send transaction who validate it ? Here I think, who can check and found that I haven't got enough money in my wallet. Example; I send 100 BTC but I have only 50.
The problem is bigger becouse in my prior transactions, refund come back on "new" wallet and who can trace all my wallet to sum how much I have in that situation. I dont speak here on double spending. I undestand that part.
2) can one transaction go by mistake in two blocks, and who prevent this ?
If you are worrying about simply sending transactions that get delivered all you need is to make sure the transaction fee is high enough.
Use something like
https://bitcoinfees.21.co/ to determine what the best fee is at the time you send your transaction.