Although Leonard didn't notice anything wrong with busting the hideout of the lone peddler and antique smugglers, it was peculiar to discover so much cash and precious metals at once in their warehouse.
While it's true that criminal gangs and the Roma tend not to trust banks, and often carry cash with them, finding such a large amount in a storehouse at a shop is certainly unusual.
However, after a simple analysis, Leonard and the others concluded that this could be because their organization might only have this one location available to them, hence, they entrusted their valuables here so that each member could relax a bit.
After all, in a criminal organization, trusting others and fostering unity and camaraderie are virtually impossible. Therefore, it is only natural for them to guard against their own members.