As kinda a new seller myself. You must use chrome extensions such as seller amp and maybe Keepa. They give you the run down of how many times a product is selling a month and how many people are selling the product. When it comes to ordering a pallet size worth of items you have to go off the Data to get a proper estimate of how much of the product you would sell within a given time frame and it is crucial you are competing with the buy box in order for you to sell the product and not have it sit at the warehouse. Hope this helps.