In my opinion, making $1,000 a month profit is very feasible, especially if you DON'T start a business, use your existing house to store everything, and use your existing car/truck to load/move everything from storage lockers. Understand you will probably spend 90% of all available free time to realize this $1,000 profit.
Here's the problem with this "business" (depending on your current resources). Making $500 or $1,000 a month is accomplishable for most people.
The primary issue with making any more money part-time or full-time is overhead.
It's easy to assume if I buy 4 units a month & make $1,000 in profit, then if I buy 8 units a month I will make $2,000 profit!
NOT SO FAST!
Here's what happens:
More units means you need a way to move them: (rent trucks, buy truck, buy trailer, etc.) major capital expenses.
More units means you need a way to store inventory: (rent storage units, warehouse, buy out-building, build barn, etc.) major capital expense.
More units means you need more money to buy/win the units: major capital expense.
More inventory means you need more outlets to sell from then your house: (flea markets, vendor's mall, store, etc.) major capital expense.
Then all the the other costs that you don't notice when you are "small time" creep in: (fuel, shipping fees, commission fees, cleaning supplies, shipping supplies, office supplies, moving supplies, repair supplies, etc.)
Dont' forget the intangibles, like the regular auction crowd might be fine with you winning 1 unit a month/week but as soon as you try to become a "player" they are going to run you up on units making your cost of inventory higher.
My point being, working out of your house a buying a storage unit or two can be a way to make a good part-time income, but upscaling the process to earn more money is more challenging then it might appear.