Assume that the borrower intends to repay the loan; the question then becomes "Is it better to have [thing I can buy] right now than to have [more things I could buy later] instead?" For major capital investments, like houses, it's reasonable to say yes. For things like consumers who keep constant payday loans but spend their money on things that they don't really want, it is less reasonable.
It's still reasonable to exclude 'money pumps' that require a minimum time to elapse, because the truest form of money pump is a series of exchanges that end up strictly worse that would all be accepted at the same time or in rapid series.
Intransitive preferences are a demonstrable characteristic of human behaviour. So why am I having such trouble coming up with real-world examples of money-pumping?
"Because I'm not smart or imaginative enough" is a perfectly plausible answer, but I've been mulling this one over on-and-off for a few months now, and I haven't come up with a single example that really captures what I consider to be the salient features of the scenario: a tangled hierarchy of preferences, and exploitation of that tangled hierarchy by an agent who cyclically trades the objects in that hierarchy, generating trade surplus on each transaction.
It's possible that I am in fact thinking about money-pumping all wrong. All the nearly-but-not-quite examples I came up with (amongst which were bank overdraft fees, Weight Watchers, and exploitation of addiction) had the characteristics of looking like swindles or the result of personal failings, but from the inside, money-pumping must presumably feel like a series of gratifying transactions. We would want any cases of money-pumping we were vulnerable to.
At the moment, I have the following hypotheses for the poverty of real-world money-pumping cases:
Does anyone have anything to add, or any good/arguable cases of real-world money-pumping?