Once you get the hang of how to win by basically using just 8 cards (three 7's, three 9's, and two 10's), you can take extreme advantage of any Merchant that plays Caravan.
Here is basically what I did:
I realized that most merchants start out with a relatively low amount of caps so you had to find some way to increase their caps so that you could take them from them in caravan.
So the obvious solution is to just sell a couple of your guns to the merchant and then buy them back. Do this as repeatedly as you can until you get low on caps yourself. Every time you sell an item to a merchant he will sell it back to you at a higher price. This is how you can actually "create" caps. Once you do this several times, challenge them to a game of caravan and win back all the caps you just created.
Rinse and Repeat. Profit.
I stumbled across this when I went to the NCR Camp Mojave and started playing Lucy. After about an hour I had over 100,000 caps and an ungodly amount of NCR cash.
There appears to be a bug with the NCR cash. Each time you sell it to Lucy and then challenge her to a game of caravan, she doubles the amount of NCR cash that she has and uses that to pay (she uses all NCR cash before using her caps) you when you win in Caravan.
I think I will replay the game without using this tactic to get infinite caps as this made the game seem really easy. Talk about never having to worry about repairs or managing your caps.