is it allowed to sell duel arena bugs of a RSPS on sythe

Yes, you're allowed to sell all rsps gold as long as it's not knownly duped.

aka I can't buy gold from someone if I know they duped it and resell it without informing the customer

Edit: misread title, but yes it's allowed

 

As long as it's not duping the gold your fine,
if your just winning the gold of another person it's fine (example prayer on bug),
If we're talking in terms of selling the bug,
you don't need to verify it with anyone, but most smaller shops get a highly trusted person to verify it to get it to sell easier because people don't trust them, but you are trusted enough to sell it yourself.

it's up to you if you wanted to get it verify but your not breaking any rules if you don't, as far as I know,

if it's a simple pid glitch (to get first hit) it doesn't matter at all