If doing business over the internet, there is only one way to be safe; use a credit card. I have only had one problem in about $10,000 in internet purchases, but that one problem was sufficient to make me glad that I had put the purchase on my credit card.
If you have a dispute with a merchant, the credit card company issues you a credit, then offers the merchant a chance to refute your charges. If the merchant cannot refute your charges to the satisfaction of your credit card company, then you keep the credit (also called charge back).
If you pay by cash, check, or MO,you have virtually NO possibility of getting your money back, even if the merchandise is not delivered. I found this out the very hard way; I sent a gunsmith in another state three of my guns, and some money to do a lot of gunsmithing. I got one of the guns back. I contacted the ATF, since he was refusing to return my registered firearms, they were not in the least interested. I also contacted an attorney in the state where the gunsmith resided, he said that there was virtually no chance of getting any money or guns back; he said the guy is out of business, he has probably sold your guns, mortgaged his house to the hilt, and you are foolish to spend your money trying to get your posessions back.
So, learn from my errors. Use a credit card. If the person doesn't do credit cards, either walk away, or make a deal where a third party can broker the exchange of goods and money. This is commonly done with gemstones, but is a somewhat cumbersome and expensive manner in which to conduct business. Hope this helps, Walt