I am a (retired) CPA and my wife, prior to her retirement, worked for the Internal Revenue Service. We have both been doing eBay for years. (Interesting agreement: She does all the selling and I do all the buying.)
Every year I have kept a spreadsheet for each sale, showing the item number, short description, selling price, cost, and shipping fee. I keep eBay/PayPal fees and shipping costs in summary.
We have reported her income each year. Of course, if we did not and we were auditied, we could have not only been subject to interest and penalties but she could have been fired. The additional tax is not significant, but it also gave her needed Social Security credits.
We have filed using Schedule C (and also SE). This does allow additional items, such as the digital camera and other related expenses, to be deducted which otherwise could not be.
As far as Sales Taxes are concerned, a lot depends on the state you live in. When we lived in Virginia we only had one or two sales per year to Virginia residents, so we did not bother with sales taxes. Since moving to Florida (after retirement) we have had lots of in-state sales, and also the state is much more aggressive about sales tax, so we do collect from any sales shipped to Florida addresses.