Potential buyers say they have been shut out of Sotheby’s big spring auctions on May 8 and 15 after the house cut standing room and about 200 seats from the sales floor. “I couldn’t believe it,” says veteran attendee Ellen Marie Donahue, co-owner of the Chelsea gallery the Proposition. She adds that she was told she could still get a ticket if she passed along her primary clients’ financial information to the house, but she declined to do so. She says the client-services department told her it had been asked to call dozens of people with the bad news. “Because interest in attending these sales is unprecedented, we simply do not have the space to accommodate everyone,” says Sotheby’s representative Diana Phillips, adding that Sotheby’s “proactively invited our most active clients” and told others they couldn’t fit when they called to inquire about their tickets. So, they won’t get to bid on that $40 million Rothko.