This is an incredibly short-sighted and simplistic view of the entire process that could REALLY land a lot of people in trouble and taking SIGNIFICANT losses on their items.
I've been teaching/practicing similar practices a long time and I have seen people make some mistakes that the OP has eluded to.
Here's the thing.
You have to know some things BEFORE you list an item BEYOND just 'lowballing and 'selling for higher' on eBay.
In fact, BEFORE you list an item (and this is what NO ONE teaches besides me) you need to know the MARKET worth of your items, formats of the item, then take the very specific deductions from there to find a SPECIFIC profit from there.
Even so, costs to acquire can be manipulated when negotiating with suppliers and dropshippers but you CANNOT do this unless you KNOW what the market worth of the item is!
How on earth can you 'lowball' when you don't even know what a LOWBALL is?!
You have to know specific data points, deductions, market worths, and utilizing expensive research tools is NOT necessary. I've been teaching how to use FREE tools to 'spy on the smartest kids in class' for years.
Again, the OP's views - although well-intended, it is too simplistic and dangerous unless you are armed in knowing how to research and find the specific numbers to FIND -- BEFORE you list all of the DATA points needed for negotiation, profit margin analysis, and market worth.
Otherwise, you're screwed.
I've been teaching this way too long to see these mistakes and stay quiet.