Seasonal Rental (3-4 months) Payment Term Question? Full payment

[Fllnids Agg]

Hi there again,

What are standard terms for snowbirds (canadians / international folks) in Florida who are renting for Jan-April?
I have a possible client who says, they have paid month-to-month like a yearly lease for seasonal in past (with a $250 deposit non-refundable to book the place).

I thoroughly checked online, most companies / local property managements show 50% at booking and 50% 45-60 days in advance. Talked to a local realtor who says, we are flexible on how they want to pay.

I am worried, what if they cancel last minute?  and we are out of tenant? 

Just want to know what are usual payment terms for seasonal rentals?

Thanks!