I respect the input of others, but I didn't see anything to indicate any bidder has put eyes on the bus. That may have happened, but none of the questions/comments indicated that happened...so I'm hard pressed to doubt the seller's "surface rust" response. My personal experience with these purchases has been positive and I've found the answers to be accurate or, at least, not intentionally deceptive.
The bus is sold "as is" meaning they won't fix anything. But the buyer does have protection, since the seller said the rust is limited to surface rust only. If the buyer inspects the bus before removing it from the lot, they have the option to back out if they find that the "surface rust" description was not accurate.
Description Warranty. Seller warrants to the Buyer that the property offered for sale will conform to its description. Any claim for misdescription must be made prior to removal of the property. If Seller confirms that the property does not conform to the description, Seller will keep the property and refund any money paid. The liability of the seller shall not exceed the actual purchase price of the property.