It doesn't matter whether you have a company or you're retired.  They key is whether you made a profit; if so, then you have reportable income.  

 

As the IRS Help page ( see link in the other post) explains, if you are selling personal items (such as household goods or clothing) for less than you paid for them, then there's no profit to report.  The IRS calls this type of activity an "online garage sale."