Substitute Tickets are tickets that a seller has offered to a buyer that replace the tickets the buyer purchased.
Substitute Tickets can also be referred to as "replacement tickets," "subs," and "upgrades."
If the substitute tickets are within 5 rows and in the same section as the original order (Buffer Allowance), the seller is allowed to offer those without buyer approval. If the tickets are outside the scope of the Buffer Allowance, then the buyer must agree to the seller's substitute ticket offer. If they do not, the seller is subject to a busted order penalty.