Caveat emptor is Latin for "Let the buyer beware".
This is your official warning -- there are bad people on the Internet who would like nothing better than to take your money and deliver absolutely nothing in return.
Even more pathetic, many sellers are simply too stupid to realize that what they are selling may be ineffective or even dangerous. Their intentions may be pure, but their results are often disastrous.
Many sellers here live in areas with laws that differ from your own. What may be legal for them may be illegal for you. Know your local laws before making a questionable purchase.
Legal recourse over international borders is almost impossible. Payment systems such as PayPal are notoriously unhelpful in dealing with fraud.
Alas, we too are not going to be very helpful. We don't have a magic ball that tells us who is naughty and who is nice. We don't know if any specific product or service is going to meet your requirements or not. This is a public forum, anyone can register and do business here.
The best assistance you have are the opinions of your peers. This doesn't just mean iTrader points, it also means comments in sales threads. That is why we specifically allow negative comments in sales threads. A free market requires the free flow of information.
But in the end, all buying decisions are yours and you must bear the burden of responsibility for them.