It does matter. You want to ensure that you use a trustworthy site for it so that you actually do end up getting the coins you bought. Check out localbitcoins. Make sure to look through the listing though an to choose a reputable seller that you can trust. You shouldn't have any issues then.
It is very difficult for someone to trust in the network without knowing this person. Perhaps only tips or slats navigator can help. Because it's not so easy to buy Bitcoin because it's not a simple currency.