As I've been delving into the PPC arena I've noticed a few things about success and failure. So far I've realised that there are two reasons people fail with PPC.
1) They don't give it a chance to work (stop campaigns too early)
2) They haven't got a budget to give it a chance to work
I've also come to realise that not every campaign will turn a profit, or even a sale.
It's all about testing a campaign, tweaking it then either dropping it or scaling it up.
You will find winners but you HAVE to endure the process of weeding out the campaigns that don't work first (and paying for it in the process).
However you CAN start with a small budget but it will take longer to figure out if the campaign is profitable or not. It'll be quicker if you can send a few hundred clicks in a short period of time.
You have to let your campaigns run to at least 100+ clicks to give it a chance of converting at least one sale.
If you've done the research phase correctly then all you can do is sit and wait for the clicks to come in and make your decision based on the results.
The unsuccessful campaigns outweigh the successful campaigns so just keep going if your budget allows! (That's why I always start with a low budget so I can keep testing new campaigns without going broke).
Anyway, these are just my experiences please do add!