I just want to clarify my post since some of you like to hate. 150% markup would be 2.5x the price at Wal-mart. Impossible. At best OP probably got 10-20% markup.
Never did I say it was wrong or bad to use Wal-mart. I owned a dropshipping business on e-Bay a few years ago and was moderately successful. Doing things like this is always about the profit margin, and selling in bulk. When you can get an actual dropshipping company to send stuff out for you, then you can have huge profit margins. Otherwise, the best you can do is find lower prices on other sites and get maybe 5-10% markup. This might turn into a few dollar of profit per sale, but if you are smart you can make good money doing this.