booking la paz-uyuni flights

the flights can fill up and will do so even more in the rainy season as road conditions become worse. It is very unlikley that rain conditions in dec or jan would make tours impossible - the water table is usually not high enough by then to cuause severe flooding on the salt.
If you book flights ahead amaszonas are ok with you cancelling in advance as long as it is at least a few days in advance . Penalties would apply if you cancelled say the day before - usually about 16% fine , although they could change this. You need to provide photocopies of your passport to cancel flights and receive a refund.

Flying Amazonas is just like all air travel. Booking 2-3 weeks in advance is much cheaper. And I agree with #1. Not being able to book a trip from Uyuni is extremely unlikely, even in rainy season. It is a desert place, after all.

thats actually a good point about the cost that 2# makes. Amaszonas sell two classes of flight with about 80 to 90% of seats sold at teh cheaper class and the remainder at a more expensive class. Both classes are identical in every way except price - obviously the more expensive ones are sold last, so booking earlier can mean you get a cheaper fare.

Good points all. I will go for early booking.

Thanks everyone.