Making transaction on the Internet is nothing new, and that is why scammers know of many different ways to cheat people out of their money. There are some ways to protect yourself from scammers, but you should never buy anything from someone you do not trust. Here are some things that you may want to do:
-Buy from established auctions like eBay, and only from people who have a lot of positive feedback. Most of them would not be willing to lose their reputation in order to scam somebody. On the other hand, users with no feedback have almost nothing to lose, and might be even creating new accounts for the sole purpose of scamming. Beware of anyone that has a lot of negative feedback.
-Do not use eGold or similar types of payments, but rather use PayPal that usually offers protection for the buyer. Sites like eGold offer no protection whatsoever, so scammers will be often using such forms of payment. There have been thousands of people being scammed just because they agreed to transfer money to an eGold account.
-Do not buy anything really expensive from someone who does not have a good reputation. There is always a risk when it comes to expensive items. If you buy something that costs only a few dollars, then you will probably not get scammed.
As long as you adhere to the guidelines above, you should not have that many problems. The most important rule is to not trust everyone on the Internet.