For the 2nd point, is googling not helpful? As in, can't the user just Google for that stuff and buy it from eBay or whatever?
But in these Facebook Groups, general 'want to buy' posts are created since there may be a brand/item that you don't know about - someone else may have found something that fits the criteria in the past.
This is a way for people to recommend items to you, tapping into their experiences & learnings and a great way for you to discover new products without the effort of trawling google/eBay/Amazon etc.