A summer to forget for the auto wholesaler threatened to stretch into the colder months.A tough summer for wholesale automobile marketplace operator ACV Auctions (ACVA -2.81%) stretched out into the first full week of September. According to data compiled by S&P Global Market Intelligence, the company's stock price took a sub-15% tumble over that stretch. Lingering downbeat sentiment on the company was exacerbated by news of a client's bankruptcy filing. Client bankruptcy bluesBefore market open Wednesday, ...