I really want to gain weight badly so I bought a weight gainer powder recommended by the supplement store salesperson. Do you recommend these?
Well, it's a little late to ask me since you’ve already bought it, but NO. I definitely do not recommend them. The idea of a higher calorie, easy to drink shake is great, unfortunately most weight gainer products are less than ideal. These products are remnants of the “high carb” 80's, back when everyone recommended eating carbs to gain muscle. Almost all weight gainers on the market contains tons of carbs in the form of sugar. That alone should be enough to make you avoid the product, but they also contain VERY LITTLE protein.
Think about these two points 1) Protein is what builds muscle, not carbs. 2) Excess sugar consumption typically leads to accelerated body fat storage.
When looking for a MRP, or even a weight gainer, look for products that have plenty of high quality protein (preferably whey), and low sugar content. Overall, the product should have much more protein than total carbs and very little sugar.