Well this is how the system works.
Remember the old days when you had points ?
The points simply made & broke the ground connection to the coil to prevent the voltage generated by the moving magnet being released till the piston was in the correct place.
Well the voltage generated in the coil is not an on/off event, it starts at 0 volts, goes up to around 1500V then drops off to 0 again.
In 1962 a mob down here realised you could measure the voltage rising in the coil and electronically make & break the ground contact.
It is called a Hall Effect Trigger ( google it ).
Atom marketed them for 30 years till the patient expired then every engine maker that was too cheap ( Briggs & Tecumseh ) to pay Atom royalties made their own trigger.
Fist off they were small circuit boards , around the size of a postage stamp & 1/8" thick & were fitted externally.
You can still buy them like that and these last almost forever.
However engine companies worked out the tiny circuit board which cost around $ 2 could be replace with a chip embeded into the coil which costs around 10¢.
This also makes the coil & trigger 1 item which reduces the assembly & inventory costs .
It also allows them to charge up to $ 100 for a $ 10 item because it is now unique and not repairable.
The voltages measured are tiny and the current is even tinier still so a cheap OHM meter shoves current down the probes and measures the drop in the return voltage and uses Ohm's Law ( google it ) to convert voltage drop into resistance .
Thus taking an Ohm reading on the primary side can destroy the control chip.
Now you can measure the secondary resistance, because the coil is also a transformer and has 2 sets of windings, a primary ( has the chip on it ) & the secondary ( has the spark plug on it ).
However as it is a single unit & not repairable measuring anything on it just wastes time & proves you have no idea about how the magneto module actually works.
You only do 2 tests on a magneto.
1) remove the kill wire
2) tug on the spark plug boot to confirm it is actually connected.
Because the system works on magnetism & magnetism travels through rust, paper, wood, earth etc etc removing rust will make zero difference to a magneto unless it is so thick the coil legs actually touch the magnets, but that willbe visually apparent because there will be scrape marks o the magnets.
So the instant some one starts talking about cleaning the rust off, you can forget about anything they say cause they are just keyboard clowns regurgitating the rubbish some equally as scientifically ignorant moron has been sprouting on the web in order to make themselves look important / smart etc.
Now back to your problem.
Without the ground wire connected and if the coils themselves have a good ground ( clean where that contact the mounts ) then it either generates a spark or it dont so as previously mentioned it works or it gets replaced.
Different coils have different chips in them so in most cases they are not interchangable regardless of weather they make a spark or not.
Finally.
The only scrap in China is what they import to reprocess or salvage.
So parts made by the OEM supplier to Briggs / Kohler / Honda that fail quality control get on sold to surplus wholesalers ( along with genuine surpluses ) and ultimately sold to cheapskates via ebay amazon etc.
OEM does not mean works it simply means it came out of the same factory.
I can buy coils direct from China for $ 5 or from Hong Kong for $ 5 to $ $20, but I pay $ 40 to get identical looking ones from my wholesale supplier because these are the ones that work properly.