Okay, this one's a long and harder to explain one, so I'm gonna give you the example that I found the bug in:

I was making a shop for my realm and the command blocks were not working. I already knew how to make a command block shop, and I've done it in the past. Here's what I did:

Button activates system
Impulse unconditional needs redstone: /scoreboard players test @p Money 300
Chain conditional always active: /scoreboard players remove @p Money 300
Chain conditional always active: /give @p diamond 1

There were no errors when running this from any command blocks, and it removes your money and does not give you the diamond. If you change the last command block to unconditional, it gives you the diamond even if you don't have enough money.

Please help