I have gotten the vault teller is at lunch or went home early, but its also at the appropriate times in most cases.
Generally I find if I am a polite pest and ask when they will be back, or what is there name, etc. It forces an answer in a polite way. This also gives them an easy out with out making them look bad.
Simply come back another time and once they get to know you a bit better they are more helpful.
No matter what being as polite and professional as possible gets you a long ways. Even if you get a bad teller or a mean teller if your always nice to them, telling them you appreciate it, telling them to have a nice day when your done, complimenting them on something mundane like a sweater or jewelery and just being pleasant does wonders.
Bank tellers get a lot of crap from people sometimes, particularly when they have to tell people they cant do something due to policy like cashing another banks check or dealing with "non" customers. I have seen more than one redneck start ranting loudly at the tellers when they wont cash a check or want to see two forms of ID or need to take a finger print etc.
When this happens however it can be a golden opportunity to get good on there sides.
If you remind the redneck that its not the tellers fault and that its corporate and there is nothing the teller can do it often calms the redneck down, you may have to listen to a short complaint but then when you get to the teller just be like, "gosh some people, not like its your fault" of course they agree with you and love ya for it, remember you and are quite accommodating of yuor needs.