Group 1 - The rise of "串串房" (quick-renovated rental properties) is driven by the demand from transient populations in major cities, leading to rapid renovations and cost-cutting in materials and construction [1] - These properties often use cheap, unknown materials that lack environmental guarantees, posing potential health risks to tenants due to poor indoor air quality, particularly concerning formaldehyde levels [1] - A typical 50 square meter apartment in Beijing can be renovated in about 10 days for a cost of 8,000 to 12,000 yuan, significantly lower than standard renovation costs which can be two to three times higher [1] Group 2 - Legal challenges arise as landlords may knowingly rent out properties with formaldehyde issues for profit, leading to disputes when tenants experience health problems after moving in [2] - The long-term nature of formaldehyde emission complicates the situation, as initial air quality tests may show compliance, but issues can arise after tenants occupy the space [2] - Current penalties for landlords of "串串房" are insufficient, and while tenants can seek legal recourse for refunds and damages, their actual losses often exceed the compensation received [3]