Done selling on eBay, they are demanding my social security number to sell

It looks like you hit a threshold which triggered your account to appear like a business.

Paypal is required to send a 1099 if you receive 200 or more payments totalling at least $20,000.  They would need your SSN / Tax ID in order to do so.

https://turbotax.intuit.com/tax-tips/self-employment-taxes/a-tax-filing-factsheet-for-ebay-sellers/L7h6uJr0i

https://turbotax.intuit.com/tax-tips/small-business-taxes/when-the-irs-classifies-your-business-as-a-hobby/L5NClTTtK

https://community.ebay.com/t5/Member-To-Member-Support/Social-security-number-needed/qaq-p/26407162

Hopefully this answers.

Its not required. eBay wants social security numbers in order to be able to report sales to the IRS. The stuff you buy new will be depreciated so that selling creates a taxable gain. Or even better, if you can't document what was originally paid then the whole sale is taxable income. Then if you buy and sell more than a few times guess what? Now you're a business. You'll need to buy a license, keep records, pay taxes. Think I'm kidding? Its exactly what they've been doing with cars for years. 

Looks like you’re considered  a business.

it asks if you are an individual or a business.  I looked at the business options. They had I think 3 categories that I did not fit in so they said I was an individual. Still want my SSN.