I have had good luck with used cranks although mine have come from in-person purchases at swaps and co-ops.

Sometimes at the co-ops crank sets are in varying levels of completeness and/or usefulness so I have had to cobble a set together - say from combining two sets or digging through the chainring bin.

Once at the co-op I was fortunate enough to find a single NDS crank arm with an exact brand and size match for one I needed to replace due to a "flared" square-tapered hole (used bike purchase). It was a different color...but I though it added character