I have question

I'm pretty sure it's banable to game the resource system like that

 

If they request a refund, that is up to you how you wish to proceed.
You could issue the refund or you could deny it. That is your call.

If they do a chargeback, you better have a strong case as to why they do not deserve the refund.

Assuming you are talking about your $1 resource, if someone asks for a refund and they have a strong case, ie: resource is advertised to work on 1.15.x but does not ... I recommend just given them the refund.
I have never sold a resource but I heard that if someone does are a chargeback and it goes thru, PayPal charges you a $20 chargeback fee, is that really worth it over a $1 resource?

 

Since spigot isnt taking part in resources plugins, its handled by the buyer and the seller themself

 

Most sellers do not allow refunds but I don't think that making them is against spigot rules.

 

Mind you, if someone charges back - regardless of the result, they lose access to all future updates of the resource.

 

Just state in your TOS that it is against the rules to chargeback on you after the plugin is bought.

 

It depends

If the plugin wasn't working at all and you had a very good reason to refund it, you probably would get the refund

But if it was a perfectly fine plugin and you just said you didn't want it anymore i'm pretty sure that's a no

I've gotten a refund from an author before and kept the download, it's up to him.