When is a property "officially" reserved for tenant?

[Charlie Gruber]

I have prospective tenant who has signed a lease but hasn't sent deposit yet.  I made the mistake of also signing lease and sending back to them before getting deposit (won't make this mistake again!)

I now have someone else ready to give me a check and sign lease today.  What is my legal/ethical obligation to first people that signed lease but no deposit yet.  In my mind until have both signed lease AND deposit property isn't reserved but feels like I'm in gray area since I've signed lease.

Not sure if it matters but I'm in Colorado.  Thanks in advance for help. 

[Nathan Gesner]

@Charlie Gruber this should be a good motivator for you to study the issue, develop a policy, and PUT IT IN WRITING!

Once the application is approved, I offer the rental to the applicant and give them 24 hours to put money in my hand. Payment must be money order or certified check so I know it's good. You don't want to take a personal check and then find out a week later that it bounced. I have them sign a "Holding Agreement" that says I've accepted the deposit and will hold the unit until a specific date, at which time they must sign the lease and pay first month's rent and anything else owed.

My policy also says I'll only hold a unit vacant for one week and then they have to start paying rent. I'm not taking a property off the market and holding it empty for 1-2 months! I sometimes make exceptions and hold a property for 2-3 weeks but that's usually only for really, really good prospects in a really, really slow market.

You also need to spell out specifically what happens if they cancel or fail to complete the transaction. I recently had a guy send us the deposit and sign the holding agreement, only to cancel a few days later. I've also had tenants put down the deposit and then fail to show up when it's time to sign the lease. Some people say the tenant automatically forfeits the entire deposit. I charge a $100 admin fee, then a daily fee equal to a day of rent until the unit is rented by someone else.