In DS9 (and to a much lesser extent, TNG), the financial acumen of the Ferengi is repeatedly emphasized. Yet they always seem to cart around physical latinum (usually in gold-pressed form in-universe for convenience and out-of-universe so the allegory is blatantly obvious).
In human history, we used to do this with gold. But then someone invented banking, wherein the gold is held in a vault (or other secure location) and you get a paper ticket saying the bank owes you X ounces of gold. Paper is a lot more convenient to carry around than gold, and can be much more secure (with proper implementation). Or it can be totally insecure, in which case you basically have gold-backed currency, though that's usually issued by governments instead of banks.
Then the banks got cleverer and invented fractional-reserve banking, where they hand out more paper tickets than the gold (or gold certificates) they actually have. Normally, this works out all right, though bank runs can be a problem.
Eventually, we got to the point where the paper is no longer negotiable for gold at all. This lends greater stability to the currency since it is no longer directly upset every time there's a shortage or surplus of gold (e.g. because a large mine opened or closed somewhere in the world). There are counterfeiting problems, particularly in a world with replicators, but you can solve that by doing everything electronically with strong cryptography, which is just a scaling up of what we do today.
But the Ferengi don't seem to have followed this process. They're still at the "everyone carries gold around in person" stage. Why haven't they invented banking or fiat money yet? I'm particularly interested in in-universe reasons, since the out-of-universe reasons seem rather straightforward to me, but if anyone has any direct quotes or other good sources, I'll take those too.