does a whole sale consultant only helps for buying or even helps the investor in selling?
Should work both ways!
It depends on how hands on you want to be and how much you value relationships (hint: they are everything in business).
The more you do to help out your clients, the more likely they are to keep coming back to you for leads. Plus there is always the chance that you will get something for helping to sell it.
A wholesaler is a middleman. You find a motivated seller, get that property under contract for a steep discount, find a cash buyer to assign the contract to, and make your profit on the difference in what you contracted the property for, and what you sell to the cash buyer for.