nice question, as all said first you have to rank up and do some goods trading and gain some reputation and learn how to trade here because their are so many scammers who will scam you. so when ever you trade use escrow serivce from the reputed escrows. and if you want to buy from exchange then , i am using localbitcoins.com for buying and selling of bitcoins, apart from their their are so many exchanges who are in this business. if you follow the all rules of this forum then no one will  call you a scammer.