French jurist said:DON'T DO IT ! Plain and simple !
Furthermore like stated above it gives bad habits to those agencies, even if they won't run away with the money.
Also, creating such habits among agencies will lead to dramas : an agency run by crooks that will take advantage of this habit to cash 7.000 USD and run away with the money.
Because if this habit takes root, here is what will happen (That will soon be 8 years I live here) : One or a few crooks set up an agency, create a nice website, place fake recommendations on tripadvisor (including negative ones to make it look "real"). The turist arrives, pays the 7.000 USD, but what he doesn't know is that the agency just paid one month to the owner.
Now multiply by 5 to 10. After one month, someone rings at the door : that's the LL who asks for the next monthly rent. The turist replies "Perrrrooo ccchooo hhééé paaguaaadooo seiissseee mesessesss de aaaddeelantehhh". You know what follows right, and you would have to fight to stay in the apartment. Meanwhile, the crooks have run away, robbing 5 to 10 times the same way = they are happy with 100.000/150.000 pesos.
Don't do it : for you, and for the future visitors !
Plain and simple
You have all the details well thought out FJ - thinking of going into business on the other side of the law per chance?