If you used PayPal to buy $1,000 worth of used books or something, why would the IRS even care about it since it doesn’t involve anything that should be reported as YOUR income?
The buy side isn't the issue, it is the sell side. I haven't looked into it that much, but here is a possible issue. Most people's regular personal belongings depreciate over time. It is fairly rare that anything in that category appreciates in value. Let's say I bought a high end computer for a $2K and then a few years later sold it on Ebay for $1K. I didn't make any profit by selling it, but Ebay has to send me a 1099K since the sales amount is over $600. If I lost the receipt for the laptop, the cost basis is zero instead of $2K