Nickb,
What Avis actually states at its' website is "At worldwide corporate and participating licensee locations, members of LatinPass and their member airlines are eligible to earn 50 miles per day on qualifying rentals. LatinPass members may also enjoy discounts on Avis rentals by using their Avis Worldwide Discount (AWD) number, L162300."

You can contrast this with what Thrifty says at its’ website "LatinPass A frequent flyer program for a consortium of 10 Latin American airlines including: ACES, Avianca, Aeropostal, Aviateca, Copa, Lacsa, Nica, Saeta & Taca Airlines:
500 miles for full-size or larger car rentals.
250 miles for economy through intermediate car rentals.
Flight segment not required. Available at Thrifty locations worldwide.”

If you are uncertain about renting a car in a foreign destination it seems Thrifty might be a little less restrictive. I think RLEWIS makes a very good point and we should heed his advise. Thanks.