There were concerns of cheating of farmers by using Trial versions of World of Warcraft, to which Eyonix responded there is nothing to fear:

Eyonix: “Since there has been some recent confusion concerning the issue, I thought I’d clarify that in order to protect our player base from abuse, we have placed some restrictions on accounts created using the promotional trial version of World of Warcraft that is available through certain magazine publications. Please be aware that these restrictions are only in place during the trial period; players who decide to purchase a retail copy of World of Warcraft and activate their accounts will be able to continue adventuring with the same characters and take full advantage of all features included in the retail version of the game.

During the trial period, characters on the promotional accounts will be able to advance up to level 20 and accumulate up to 10 gold. Use of the auction house and mailbox, player-to-player trade, and access to the in-game chat channels will be unavailable for the duration of the 14-day trial period”