Why are some on my Traders out of cash ? and when do they get more?

i hadthe same problem and first time didnt notice and gave away an item for free lol broke people all over skyrim

You can wait a day or see other vendors. Or buy something from them.

It's realistic that the street vendors don't have thousands of gold to buy all your stuff.

Because people are not infinite money sinks in real life? Wait a day and they'll get more cash.

Start bartering. If you're a mage, buy all the expensive soul gems before you start selling your stuff. There are anologs here for almost everyone with a crafting profession.

Trainers are your best friend too. Barter for training = win.

Living economy