Did I say that the sales is what makes me purchase a game? No? Ok then.
They are however a good indication of the quality of a product. Common sense that loe quality products simply dont sell.
It's a lot easier to take that serious than a site with mostly "best game evar!" "Worst game evar!" reviews.
Are you 100% sure about that? Bought some broduct from Apple recently? Sales are not the best way to measure quality. Measuring quality is the best iway to measure quality. In other words, taking something like the I phone 5 or what ever is the newest model and comparing it to the competition. Or in Fallout 4s case, taking it's dialog and comparing it to Fallout 1 and 2. And there can be no doubt that that quality of the dialog was of higher quality in the previous games, that Fallout 1 and 2 have been also the better role playing games offering you more oportunities to role play and so on.
Sales to measure quality? In my experience it is way to easy to sell people mediocre products as quality. Most of the mass market works on that principle. And that's what the main job of all those marketing gurus are today. Look at Fast Food for example, like Mc Donalds. Probably one of THE most succesfull food franchises out there. Is it the best indication for quality food though? I would say no.
Bethesda and a couple of other AAA companies are game developers creating products that which are meant to be consumed in the way how you treat a fast food product from Mc Donalds or Tacco Bell.
That's not always a bad thing! I love fast food, at least sometimes. And I can enjoy mindless entertainment. And I would say that counts for most people here on NMA. Thing is, don't sell me a Mc Donalds burger as filet mignon please.
I'm absolutely 100 % sure that sales indicate if a product is good quality than a grouping of mostly not even well thought out reviews. Mosts just "game suxorz! 0/10" nonsense that shouldnt be taken any more serious than mindless positive reviews.