like it appears they have, than you shouldn't be responsible for replacing them. That's just universal return policy everywhere in the world - you can only return merchandise in the condition it was received. If I alter/damage/change something on a product I buy, new or used, it's mine. No matter what. The buyer should know that. Unless there's more to this I'd say you're in the right to tell the person they're out of luck and return the altered links to them. If they threaten you with a bad reference I'd talk to the mods of whatever forum you're concerned about.