I am not a fan of gambling mechanics. The enchantments and infusion rolls are already a gamble.
And story wise it would make no sense for him to always be there, since he said he goes scavenging. So him only appearing in certain intervals is fine, just the spawn interval being bound to real time/date is unfair for some players.
And the inventory refresh for vendors currently gets exploited by changing the PC date/time, which could also be fixed if it would be refreshing after X ingame days instead of real days.
Edit: i opened a suggestion/feedback post for this: Vendor inventory refresh and Finley spawn