Advertising is a complex system, simply putting money in a pot with a default setup will not work. Thousands of merchants are advertising for similar or exact products. You need to either study up on advertising and adwords to have full knowledge. For example it can take 60 hours of training to know the basics of adwords. Or hire someone who is an expert in the field and does it for you. As for Facebook vs Adwords, I can not comment but I highly recommend Google Shopping as the buy intent is pretty high. People see your ad and if the price is right will have a high conversion rate. Hope this helps.