I personally do a fair amount of buying broken and selling fixed. Sadly they are right on about the lack of available schematics out there.
I worked as the head service tech for a big welding supply chain and Even then the manufactures would not give out schematics that were of any real use.
Their stand point was, If we give you a schematic for a circuit board you will fix the $2 component on it and get $40 shop labor for it. The manufacturer will not get anything.
If you dont have schematic you will have to replace the whole $1000 board (That has about $50 in actual manufacturing parts and cost into it) but you will still get the $40 shop time for it.
Or perhaps you then can talk the customer into buying the latest and greatest engineering failure they came out with!
Win Win for the dealer and the manufacturer!
But not the customer. Sorry he does not actually count in business financial equations now! (he always wants more and better for less. And thats highly counter productive to actual profit!)
If you start doing the buy broken and sell fixed, expect about 60% return to service on the stuff you buy. That is, 6 out of 10 items will likely need only a small repair and 4 out of the 10 will not be practical or cost effective to repair. But they do then become great parts donors!
And above all do your market research on the actual resale value of the item you are planning to buy and fix.
I pick up industrial equipment every chance I get. When it dont work its worth around 5 to 10% of new. Repaired its typically worth 20 - 50% of new. Down side is spending $500 in a machine of some sort and hoping you will get the 20 - 50% ($2000 - $5000) of new return on it within a year or two.
And not just have $500 yard ornament with a $1000 in new parts sitting there doing nothing!
I got me a few of those!
Anyone want to buy a few 600 amp three phase welders? Or some 10 hp circulating pumps? How about 500 high efficiency solid state light ballasts that run on 277 volt, for the standard 4 ft fluorescent bulbs?
I'll give you a super deal!