This is an interesting proposition. Is there a difference in taxing a new item versus a used one. Are we supposed to report all our garage sale purchases to the Indiana IRS?
And I don't believe you as the seller are obligated to collect tax unless you do sell more that a set dollar amount in a year.
eBay is an interesting case. Some of the sellers are indeed those of us getting rid of garage sale type things. Plenty of others are a store front though. I believe eBay has chosen to collect the tax on behalf of everyone.
Ebay used to be a lot of selling used stuff, now it's a lot of store fronts and chinese crap.