By name: Scam Pattern Catalog description: Use during scam detection to recognize Berlin rental fraud patterns. Reference before classifying any listing as ok, review, or block.
Hard Block Signals (weight 0.8+)
These are near-certain fraud. Auto-block without LLM confirmation.
- Western Union / MoneyGram payment requests in any form
- "Send deposit before viewing" — Kaution vor Besichtigung überweisen
- Bitcoin / crypto / Kryptowährung payment requests
- Landlord-abroad framing — "Ich bin im Ausland / im Urlaub und schicke die Schlüssel per Post"
- Keys by mail — offering to mail keys without an in-person meeting
Strong Signals (weight 0.4–0.6)
Require at least one of these + another signal to block. Single occurrence = review.
- WhatsApp-only contact — "Bitte nur per WhatsApp / nur Whatsapp" (note: phone number in description is normal on Kleinanzeigen — this signal is about exclusivity)
- Price >50% below Mietspiegel for size + district (see berlin-context skill)
- Airbnb framing — "flexible stays", nightly rates mentioned
- Google Translate artifacts — grammatically broken formal German (e.g., "Ich brauche ehrliche und sorgfältige Mieter")
- Multiple portals, same description, different photos — coordinated scam operation
Moderate Signals (weight 0.2–0.4)
These alone don't classify a listing. They raise the threshold for ok classification.
- Price 35–50% below Mietspiegel
- Ablöse >€2,000 for used furniture
- Kaution >3× cold rent (illegal, §551 BGB)
- Landlord name is a generic English name ("John Smith", "David Williams", "Mary Johnson")
- No address given, only "Berlin" with no district — common for legit listings but lowers confidence
- Listing is very old (>90 days) at an unusually low price
Swap Signals (filtered, not scam)
Not scam, but filtered by deal_breakers config.
- Keywords:
Tausch,Wohnungstausch,biete gegen,suche im Tausch - Listing requires a counter-offer property
Portal-Specific Notes
Kleinanzeigen:
- Phone numbers in description: normal for private landlords — weight only 0.15 (not 0.30)
- "Nur Selbstnutzer": legitimate signal, ignore
- Very low-priced listings (€300–500) for large flats in central districts: almost always scam
ImmoScout24:
- Premium-contact wall on private listings: unusual, flag for review
- Agency listings with "Provision frei" but then mentioning fees elsewhere: flag
Scoring Logic
total_score = sum of triggered weights, capped at 1.0
block if score >= 0.85
review if score >= 0.55
ok if score < 0.55
LLM judgment is the last layer — invoke only when rule-based score is in the 0.40–0.84 range.