If I rent in Panama, how can I make certain it's not a scam?

First of all, it is advisable not to rent  from abroad.  Wait to get into the country you want to visit; and the best idea is to stay at a reputable hotel the first night.   That way, you see and experience the area and verify that it meets your requirements, including for safety.  After that, you can start your process of renting, but not before you have specific references from the owner or the authorized person, such as the...

First of all, it is advisable not to rent  from abroad.  Wait to get into the country you want to visit; and the best idea is to stay at a reputable hotel the first night.   That way, you see and experience the area and verify that it meets your requirements, including for safety.  After that, you can start your process of renting, but not before you have specific references from the owner or the authorized person, such as the owner's real estate salesperson, relative, friend, attorney, or even, your hotel. 

Get additional references from the police department, your embassy, and any other contact you have that knows the area.

On your visit to the site you want to rent, it is best to go and check every room, the electrical connections, the plumbing, A/C units and every detail, and make a checklist of any problems or irregularities, signed by the authorized person.

It´s also a good idea to verify the neighborhood and check if it meets your standards of cleanliness, if there are dogs walking on the street, noise, and other considerations.  Ask around.  Unfortunately information regarding who owns the property you're considering renting cannot be obtained on-line unless you are registered, but a well-established law office, real estate agent or notary public can verify this information for you.  There is an office to call: ACODECO  (Autoridad de Protección al Consumidor; "consumer affairs") from which  you can get information as well.

Make sure you understand everything you sign.  If you do not speak the language fluently, to avoid any future misunderstandings, ask for a competent translator you trust.

Today, Panamá offers several resorts for vacations in the "interior" (countryside) as well as the city of Panamá.  Hotels are already checked and of prime quality.  There are also some that offer "time sharing", like the Gamboa Resort, which is a very nice place for vacationing surrounded by nature and with special tours, situated approximately one hour (depending on traffic) from the city, but the peace, quiet and nature are beautiful.