For the purpose of PST/GST, if you are registered, you must report ALL sales, whether you collected taxes or not.
If selling from within a province that charges sales tax, you must register as a vendor and collect/remit sales tax (PST) for sales effectuated within that province. You can choose to not collect PST but you must still remit it. You do not have to charge/remit PST for sales outside of that province.
Frequency is monthly, quarterly, semi-annually or annually. In BC the vendor commission just doubled to 6.6%, making monthly remittance more attractive:-)
If your annual sales exceed CA$ 30,000 per year, you must register for the goods and services tax (GST) and collect/remit GST for sales effectuated within Canada. You can choose to not collect GST but you must still remit it.
Frequency is monthly, quarterly or yearly. If you are expecting refunds on a recurring basis, choose monthly filing. I would think that most Canadian eBayers are in a refund position every month.
Once a year, from the income tax side, you must report ALL sales and gross profits. You don't HAVE to report all expenses or take depreciation on assets, but are best advised by a competent accountant. Normally, one would declare all expenses but that's not always the case.
Registering for PST makes sense as you can then purchase your goods PST exempt.
Registering for GST makes sense as you can then claim back the GST paid on your purchases, including office and vehicle expenses, etc.
Personally, I would recommend registering for GST even if your sales are only $100/year.
Bernie