Ask for a copy of their operational permit.
Ask them how they are paid; if they say all to a non-Indonesian account, be very careful.
Ask them who owns the villa (is it Indonesian - if they say foreign, foreigners can not own villas in Bali, only Indonesian citizens and companies can).

Only pay a deposit, not the full amount is as best as it will get as villas are not like hotels with excess rooms to be able to take "no shows".

Don't book with an agent, they are generally dishonest, book direct with the villa. Agents / management companies will often tell you they have an operational permit for their villas, but Indonesian law requires each villa operation has its own license.

They are closing unlawful villas, do not get caught out!

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