Yes, it is risky, it is even riskier buying privately, 'from a man' because you have little or no warranty and plenty of possible problems.
If you need to purchase used I suggest you look on Amazon, Ebay or a similar trading company in your country.
Amazon and Ebay both have safe guards in pace and most of their commercial sellers offer at least some sort of exchange/return/refund policy.
Basic rules:
ALWAYS check the seller feedback, the more items they have sold and the more positive feedback they have the better.
CAREFULLY check the description and your E-mailed invoice, make sure they match, also put the page on your Favourites so you can refer to it later if there is a problem.
In many countries it's safer to use a credit card rather than a debit card for online transactions.
If an offer seems to good to be true it probably is, move on and look elsewhere.