Try sell the most popular things in the world, thr indemand thigs, Like cellphone.You can have a great profit in it. But if you sell make sure that it is lesser than the mall price, The cheaper the more customer comes.
Yeah something like that would give him quite a good success rate if he sells the things a little cheaper than the markets and for that he would have to get his things directly from a company and if he will be able to do that then he would be able to make a great online store i'm sure.