Here you can see the list of suspicious contacts identified by the automated system. Hover your mouse over the text in the "reason" column and find out why the site has included a certain number in the blacklist. By the way, if the phone number of the author of the ad is suspicious, you will see a warning on the ad page.
Negative feedback in comments
Placing ads in multiple areas
The rental offer is priced much lower than the market price
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