Upstart Holdings' (NASDAQ: UPST) stock price tumbled 12% on Aug. 9 after the online lending company posted its second-quarter earnings report. Revenue rose 18% year over year to $228 million, but missed analysts' estimates by $7 million. Its adjusted net income plunged 98% to $1 million, to $0.01 per share, which also missed the consensus forecast by $0.07.\nIts adjusted EBITDA (earnings before interest, taxes, depreciation, and amortization) declined 91% to $5.5 million. On a GAAP (generally accepted accounting principles) basis, it posted a net loss of $29.9 million, compared to net profit of $37.3 million a year earlier.\nThose headline numbers were disappointing, but they had already been partly telegraphed in its preliminary earnings report on July 7. And a deeper dive reveals four additional red flags.\n1. Upstart management has a bleak outlook for Q3\nFor the third quarter, Upstart expects its revenue to decline 25% year over year to $170 million, compared to analysts' expectations for 8% growth. It also expects to post an adjusted net loss of about $9 million and for its adjusted EBITDA to come in at break-even levels.\nOnce again, Upstart mainly blamed rising interest rates, which caused people to take out fewer loans through its platform while prompting its lending partners (banks, credit unions, and auto dealerships) to take a more prudent approach to funding those loans.\n2. Upstart is questioning its own business model\nUpstart initially attracted a lot of attention for two reasons. First, it analyzes nontraditional data -- including a customer's educational history, area of study, standardized test scores, and work history -- with a cloud-based artificial intelligence (AI) platform to approve loans.\nSecond, Upstart offers a wide range of loans on its website but doesn't usually fund them from its own balance sheet. Instead, it acts as an intermediary for its lending partners, which then fund the actual loans and pay Upstart fees for accessing its platform.\nThat business model exposes Upstart to less credit risk, but it also creates a bottleneck by making it dependent on its lending partners for fresh loans. To overcome that bottleneck, CEO Dave Girouard abruptly announced during the second-quarter conference call that the company would start to "leverage our own balance sheet as a transitional bridge to this committed funding."\nThat's a risky move because Upstart has already ended the second quarter with an elevated debt-to-equity ratio of 1.5. It still held $790 million in unrestricted cash, but that liquidity could quickly dry up as revenue growth decelerates and its losses widen.\nGirouard said that while it "doesn't make sense for Upstart to become a bank," it needed to "upgrade and improve the funding side" of its marketplace as interest rates rise. In other words, management is starting to question the resilience of its own business model.\n3. Upstart is seeing declining loans and conversion rates\nUpstart's number of bank-partner loans increased 12% year over year to 321,138 in the second quarter but still dropped 31% sequentially from the first quarter. Its conversion rate, or the percentage of its total inquiries that are converted into actual loans, came in at a mere 13% compared to 24% a year earlier and 21% in the first quarter of 2022.\nThose declining engagement rates explain why Upstart is so desperate to fund its own loans. They also suggest that its smaller competitor, Pagaya Technologies (NASDAQ: PGY) -- which provides comparable white-label AI services to financial institutions instead of acting as an intermediary platform for loans -- might be taking a smarter long-term approach.\n4. Management initiated pointless buybacks\nAs Upstart faces a grueling slowdown, incurs wider losses, and takes on more credit risk, it's also buying back more shares. In February, it announced a $400 million buyback plan. It didn't repurchase any shares in the first quarter, but it bought back $150 million worth in the second quarter.\nThese buybacks are arguably wasteful, since all that cash could have been used to fund its new loans, reduce its debt, or simply expand its platform. Upstart bought back 4.4 million shares (at an average price of about $34), but its number of weighted-average outstanding diluted shares only declined 1% sequentially and actually rose 1% year over year to 94.5 million.\nTherefore, Upstart is likely using these buybacks to offset the dilution from its stock-based compensation expenses, which jumped 86% year over year to $55.4 million in the first half of 2022, instead of actually returning that cash to investors by reducing its float.\nUpstart deserves to stay in the penalty box\nUpstart's stock might look reasonably valued at three times this year's sales, but that price-to-sales ratio is still pegged to analysts' expectations for 12% revenue growth this year. Those estimates could be reduced after Upstart's disappointing second-quarter report. For now, it deserves to stay in the penalty box until it stabilizes its core business.\n10 stocks we like better than Upstart Holdings, Inc.\nWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.*\nThey just revealed what they believe are the ten best stocks for investors to buy right now... and Upstart Holdings, Inc. wasn't one of them! That's right -- they think these 10 stocks are even better buys.\n*Stock Advisor returns as of July 27, 2022\nLeo Sun has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Upstart Holdings, Inc. The Motley Fool has a disclosure policy.\nThe views and opinions expressed herein are the views and opinions of the author and do not necessarily reflect those of Nasdaq, Inc.