Profit = Selling Price - Cost of Goods Sold. Cost of Goods Sold = original price of goods + marketing costs + labor cost + facilities costs.

This isn't the precise formula, but it's close enough. It's still a good ROI, but it's definitely not scalable as this was a liquidation. You also have to calculate the tax rate on the sales as well.

If you're grossing $10,000 and you spent $2000 on records, 8 hours of labor (paying yourself $15 per hour) + the cost of the facilities (let's say $100 for the day) and $150 on marketing.

You'll still pay sales tax on the full $10,000. Let's say your sales tax rate is 8%, that means $800 in sales taxes. So now, you're at $9200, so now we can subtract your costs, which, according to my hypothetical approximations total $2370. If you want to exclude your labor cost, you can do that, but it'll still be taxes one way or another, depending on how you claim it.

So your profit is $9200-$2370 which is $6830. For a short term capital gain (which is what this is,) the rate is approximately 25% for Federal, however you also have state capital gains taxes (it's either taxed as ordinary income or as a capital gain,) which will be about 7% (depending on the state), but that 7% is taken off the total gain of $6830. (25% + 7%) of $6830 = $4645.

From the $15 per hour you get paid from your wages, you'll then get to pay social security, self-employment and medicare taxes on top of the federal income taxes. You can avoid this by not paying the salary, but you can't work for free in the eyes of the IRS.. you'll either pay the tax on the wages, or the total gets added to the profit and taxed as a capital gain. Of course, you'll get a slight home "office" deduction for using your backyard as a facility, of course that gets offset by the facilities fee you've earned (and will be taxes on.) It's cheaper though, to charge yourself the facilities fee because that comes off the capital gain, which lowers the taxes on the gain, while only nominally increasing your personal tax (due to deductions.)

Let's just round the total profit at $4600.

So, $150 in Facebook ads to earn $4600.. still a pretty nice ROI, but it certainly isn't $10,000.

We all know the seller isn't going to go to this extreme in either paying or reporting this income to all the jurisdictions involved, but when calculating ROI or other things upon which a business is based, it's a little disingenuous to claim "making" $10,000 when in fact, that number is far less. But I get it, $10,000 makes for a nice headline.