...but don't know when you want to leave? If you spend considerable time in Mex. and are not sure when you want to return...what do you do about airline tickets? We are not going to try to get a visa right away (and I know I will be at the mercy of immigration) but do you get a one way ticket? Do you just book something like a 60 day stay and just pay the fare change difference when you decide/have to leave? Am I the only one who only plans about a week out? I never thought about it...until I started to look into airline tickets...
When I arrived I had a fully refundable Aero California Tijuana -> Los Angeles (or suchlike) ticket in my hand. They never even looked at it, but it was there in case they did. Once I knew I was staying, I just cashed in the ticket.
If you enter Mexico with an FM-T then immigration has the right to ask you to see your return ticket. An FM-T is the tourist permit that airlines get you to fill out while on the plane. Immigration can also question you about where you are staying. If you plan to live here it's wise to get an FM-3 (rentista) before you arrive, that way Immigration has to be nice. You will also (likely) have an easier time renting if you have an FM-3.