Registered or not you are a business if you buy and sell goods or services with the intent to profit (even if you don't).
If you are ONLY selling "personal effects" up to a certain limit CRA don't care (not sure of the amount, possibly $2000) and actually under normal circumstances people take a loss when selling personal goods (example, you are moving across the country and you sell all your furniture etc.)
There are a number of guides available on the basics of operating a small business and how to properly do the required accounting.
In the most basic terms it good like this...
Sales less cost of goods less expenses equals taxable income, there is a line on your tax return where you report your Gross Sales and Net Income, you need to support these claims with detailed financial statements. Don't be scarred by the "detailed" part, a small sole proprietor business could have financial statements on a couple of sheets of paper.
In reality accumulating the numbers is the only way you really know if what you're doing is worthwhile, always interesting to calculate your real hourly pay just to see how working at McDonalds while not as "personally rewarding" might be better financially!
Ben

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.