Have a great time, as well. I would reccomend that since you have time before you go, read up on carpets, visit local stores so you have an idea what to look for and the prices for same, as well as who are chiselers locally, and only then take the plunge and perhaps buy a carpet over there.
You never know if your "guide" is reputable if you know absolutely nothing, and you may wish to dispense with one altogher.
Remember, you must buy from a locally reputable dealer, because you may have no recourse if you buy a rug, and you get shipped a differnet one!
I do not think that AMEX, etc. will help you as they have a 150 mile radius limit within your home, I think.
Perhaps you can take a picture and have it developed and signed by the merchant before you leave, that you are to get that particulat carpet, if you are not going to take it with you.