Here, we have a low-baller who seems oblivious about how low-ball their offer is. The seller made two separate listings, one for a table and another for a four-chair set. The buyer, not having seen the listing for the set of chairs (understandable), offered $125 for the table and chairs.
However, the seller informed the buyer that the table and chairs were a vintage set and wouldn’t let them go for less than $260. If you don’t believe the seller, there’d be no point in trying to disprove their claims, especially if you don’t have any proof. Here’s a lesson to any online shopper: if you have doubts, just leave the conversation.