I see the merchants are supposed to refresh their inventories every so often (73 or 79 in game hours are the numbers I have seen) but they are not doing it in my game. It's not a game killer but eventually I may run into a bullet issue I suppose and it would be nice to get a different selection of weapon mods.

Has anyone else run into this, and perhaps have a trick for getting the inventories to start refreshing as they are supposed to?

Try to "wait" in front of them a few hours (works for me at about 3-4 hours waiting after the 72 game hours), should work...
svcks if u play hardcoe, but hey at least u get fresh ammu

Some merchants will not refresh their caps or get rid of items you previously sold them, but they should get new stock every so often despite being at not refreshing their caps or dumping your stuff you sold to them. Chet in goodsprings always seems to refresh everything after a few days. Also, the vendortron at gun runners will consistently refresh inventory and caps. Merchants that pose some problems are alexander at 188 trading post (who never resets caps) and cliff from the dinosaur (he never drops supplies you sold to him)

Yeah, in my game no-one is refreshing anything: not caps, and not getting fresh items. Chet hasn't gotten anything new since the start of the game. Ditto for the Vendortron, now. I don't care if they dump stuff I have sold to them, but not getting any new stock is a bit of a pain.

I will try the 'wait in front of them' thing next time I have a chance.

I had this for the first 90 some hours with Chet. However, i don't know what changed but he finally refreshed at some point. It might take doing a mission or two. I really hope they fix this problem along with the other issues. If it happens again I will also try the waiting 3 or more hours in front of the merchant fix.

I come across this sometimes and id swear they refresh every monday. I normally keep waiting ( even for 2-6 days ) in front of them and also usually stop waiting at 9am which seems to be the best time and this always works.

Waiting in front of the Vendortron got it to refresh its inventory. That at least gives me a manual workaround, thanks.