Perhaps it depends on the quality of moderation for your Nextdoor area. But those issues you listed are separate from the buying/selling part of it anyway. I’ve generally found Nextdoor & Craigslist to be sufficient.

How does it compare to nextdoor & craigslist?

That doesn’t prevent users from changing account passwords though right? Say you give access to someone to manage your social media (or some other important account), they could log in and change the password and email and take over the account.

Do you know of a way to protect against employee/partner sabotage?

Doesn’t that mean everyone has admin access to the full database and all accounts? You’re putting full trust in everyone that no one will make a mistake, or purposefully sabotage the db or accounts.