(1) These days, SPG, HHonors, Marriott, etc. often have a prepaid direct booking. You prepay like you would on Priceline, but you get elite benefits and points. Rate is obviously higher than Priceline, and usually (but not always!!) lower than a regular post-paid rate. I often find that the prepaid rate and the AAA rate are similar, with the AAA rate offering 24-hour cancel. Therefore, I almost never book prepaid rates outside of the occasional Priceline stay where I don't care about status/benefits.

(2) You usually pay at check OUT, not check in. You might see a hold on your credit card for the total amount plus a little for incidentals, but they don't actually charge the card until check-out. (Thinking normal Marriott/HH/SPG stay here...B&B's and other kinds of stays might do it differently.)

(3) I don't understand why you'd WANT to prepay, unless it's saving you a lot of money vs. other options. If you're trying to pay for another guest, there are other ways to do it. Prepaying usually kills your flexibility...the rates are often nonrefundable and nonchangeable.

Kind of need to know more about your situation...