On the black CS 3.7 I didn't see in ad disclosure the paint was not original nor they were painted by the seller. If that is true then I would ask for paperwork of what company who did the work and what process was followed to finish the CS 3.7.
I'm going to restore some CS6. The process will be documented with paint/clear coat used. If done correctly a pair would cost between $1500-$2000 depending on material chosen and labor.
If you were painting multiple sets of speaker the price would drop significantly.
A few quarts of high quality automotive paint will cost $250-$400. Add all the other necessary materials and you will be at $750-$900 very quickly.
Preparing cabinets and sanding will cost $300-$400 then you have the painting.
My point is if the painting process is done professionally with high quality paint this would increase the value. If done by some obscured person with no paper trail then I would proceed with caution.
In this example if the CS 3.7 are purchased for the asking 4K then I would have them professionally restored around the $1500-$1700 price point which would put you in the $5500-$5700 price point.
Well below the market average and for a mark free cabinet to enjoy and if you sell you have all the paperwork.