I use prime also but usually only buy prime items.If products are not here on time I give them a call and ask them what am I paying for if it is not here on time.Needless to say I have made more than my prime membership cost by getting the items free.One item was around $200.
Many states (29 according to Amazon plus DC) now collect tax through Amazon as I found out by buying something for my parents who live in IL.
I need to pay attention and hold them accountable myself. Often one or more of a multiple item order will not show for a week.
I was about to purchase something on e bay the other day.. when I got to check out, tax were added. I backed out and went with another seller of the same product , but no taxes added.. Saved me about $7.00