I would assume anyone that doesn't have the means to make an in game transaction to themself (aka, owning a house) would not have enough money worth stealing. I'm sure there are a few idiots out there, but the majority of people, especially level 50's (never trust a level 1 or level 20 toon) would never risk the reputation of taking someone's 25 gold
Once you own a house, this becomes a much simpler thing. Although you can't actually store money in a vault, you can get around this by having a merchant and allowing others to withdraw money from your merchant. A house costs about 1.8 plat or more to get started (basic house, porch and merchant), so if this is out of your reach, best to just ask a guild mate or something to do a transfer for you. I've done this for others probably a hundred times, usually not knowing the person. You might get burned, but more often then not, the person standing there will wait for you to return...and if they are nice, might even add a little extra to it. If someone gives me some small amount of money for a transfer, chances are I am going to up the amount a few hundred gold.