Is there a determining factor when it comes to how many sockets can be on an item.. I ask because as of today (not sure if the patch borked it or not) I can't seem to roll 2 sockets on a helmet where as I was able to without too much difficulty on my previous helmets. I know level is a factor but the item i'm trying to reroll is higher than the helmet i put 2 sockets on before. I also ask because I have spent 50k+ just to get 2 on there unsuccessfully. I've googled and havent seen a break down, so I wanted to check in and see if there was a breakdown as to how many sockets each item can have and at what point they become available (whatever the determining factor is).

Also I see quality stars on items (top right of item). Coincidentally I saw the helmet I have 2 sockets in (level 36 - rare - 3 star quality), and the helmet I'm working is level 43 - rare - 2 stars. So what are these "quality stars"?