1 hour ago, DGLaderoute said:S o a Crane samurai with an interest in gambling in, say, Ryoko Owari may very well end up borrowing money from commoners, who are themselves vassals to Scorpion lords.
Gambling is somewhat different than trade.
A samurai with gambling debts might turn to others for a loan, but he'll do so on his own initiative - not the potential lender's - unless someone with a ulterior motive who found out about these financial struggles intends to get leverage over him (a typical Scorpion ploy). Those he's indebted to due to gambling misfortune might extend credit, but that's not a loan. Regardless, this is not commerce unless the indebted samurai tries to offer some of his belongings to square his debts (and this will likely be construed as a gift or a favour in order not to suffer social stigma).
Trade samurai are involved in tends to be shrouded - it's looked down on, so certainly when it involves transactions between individuals (not treaties or large transactions) it's handled discretely and samurai pretend it was something else entirely. Gambling on the other hand carries no such stigma and can be done openly and publicly. Gambling debts can be acknowledged without shame. Welching on a bet is a major no-no, of course.