Cory Tschogl says she has an Airbnb squatter - a guest who rented her Palm Springs vacation condominium, then stopped paying rent, refused to leave and threatened her with legal action. Although Airbnb and similar platforms use reviews of hosts and guests to try to weed out bad players, and require credit card information from guests, those systems are far from ironclad. [...] although Airbnb has a $10 billion valuation and handles more than 600,000 temporary rentals worldwide, it's still a startup whose customer service sometimes seems to lag. Tschogl, who works as a rehabilitation therapist for blind and low-vision people, was priced out of the San Francisco housing market, so she bought a one-bedroom condo in a gated Palm Springs community 18 months ago. The texts threatened to press charges for "blackmail and damages caused by your negligence and malicious misconduct, including $3,800 PID Espresso machine as well as medical bills for my brother's hospital visit after he got sick here drinking unfiltered tap water." The guest, whose Airbnb "verified ID" says he is from Austin, Texas, did not respond to e-mail requests for comment and his cell phone did not accept messages. Copies of her e-mails with Airbnb, reviewed by The Chronicle, showed several delayed answers, for which the customer service representatives apologized.