Totally correct - provided - that all transactions actually took place and are supported by documentation.
Usually, people post questions to get answers to a problem they - or one of their friends - don't know how to handle. To me, you questioned whether the gap between actual income and the minimum required to qualify for a program could be closed - in theory - with income that could have been generated by selling on xyz's websites. Therefore I tried to politely caution you not to create "theoretical income" for a real-life application. Sorry for the inconvenience caused.
And by the way, if somebody is regularly selling items on the internet, such income is taxable. And reporting it under Schedule C as a sole proprietor is an advantage since he can deduct the cost and expenses related to the sales transaction. There is however a fine line when it comes to selling personal items. As long as you are just selling used personal property such as a computer, furniture, you can assume that the cost of the item equals the price you sold it for. When you start trading - buying items and selling them commercially - the valuation methods come into play and those sales must be reported. A very interesting niche in that market are "collectors". In general, you can sell your used car online without generating a profit. However, if you are a collector who buys cars as collector items, hangs on to them until their value increases, he is considered a commercial trader and fully taxable. Since those items are usually high in value, it is preferable that such people operate under the legal and financial protection of a legal entity.