I had a customer that filled out a 4473 I did a e check and was denied, customer claimed he has always been delayed but not denied. He did not use his ss#, can He retry with his ss#?

You’re likely to get some differing opinions on this one. I always advise my clients to NOT do a second 4473. You now have reason to believe that they are a prohibited person (you just witnessed heir denial) and therefore you shouldn’t start the process again for any firearm with them. Also, there’s a specific appeal process that they can go through to overturn their denial if it is incorrect. I can only imagine the potential liability if they were approved the second time and they did something wrong with it - yes, you got an approval, but you’re also on record with a denial. Please have them appeal it on their own and put them on your “do not do business with” list (including folks at the same address).

I cover some of this in this episode of my Trigger Words podcast on firearms law: https://itunes.apple.com/us/podcast/trigger-words-w-ryan-cleckner/id1299836235?mt=2&i=1000399846002
and I cover these topics in my articles and courses at RocketFFL.com

If you listed the NICS NTN# you can call and add in the SS# into that transaction and see if it changes the outcome.  
This is done as an addendum to the existing transaction not starting a new one.

Denial does not mean you mean you have a reason to believe that they are a prohibited person. Question 19 covers reasons to believe they are prohibited. I have seen plenty of denials and not a SINGLE one was a prohibited person. So statisitcally, when I see a denial it means get a UPN or LTC, or next time put down your SSN.

Now my own policy is if you choose not to provide the SSN (and are not NICS exempt)  do not complain if it does not come back proceed.

This

So should he try again?

No Federal law or ATF regulation prohibits a buyer from trying again.
In fact, I had a young man born in Japan, Canadian citizen, in US on a temporary visa get denied on his first attempt despite having a Texas hunting license (an exemption). He was 18.....too young for a Texas LTC that could exempt him from NICS.
He appealed and after three months with no word from ATF, he asked to try again. Denied a second time. Another three months and he gets his U.S. Permanent Residency, Denied a third time. Three days later ATF calls to reverse the denial.

I'm not the least bit worried about explaining to ATF, I just keep his denied 4473's on file like I'm supposed to.

That depends on your policy and how you handle folks who do not put SSN down and then want a do-over.

while i have never had a denial

i would not redo the  NICS check
i would ask them to appeal

I just had my first denial, guy is an older man(63 years old), has transferred firearms through me before, last time was around two months ago(he put his SSN on the form)
Today he did not put his SSN on the 4473, ran an E-check and after some computer/NICS website issues, he was denied.
We were closing for the night so he left and I told him I woudl contact him in the morning.
I do not want to do the wrong thing,but it does seem that running his info again is allowed.

Why doesn't a guy who knows he gets routinely delayed  not take every possible step to avoid future delays. Like using a social, or applying for a UPIN

I was denied once.  FBI sent a letter saying they screwed up to me a few days later.  It instructed me to bring the letter to the FFL and pick up my gun.  Also advised me to get a UPIN, which I did.  No problems since.  Denial does not equal a prohibited person.  I have read about a lot of FFL's that claim to call the law on someone when they get a denial.  Maybe they should stop and think a bit before they do.

Where did you read that?

Ya, I would like to hear where that came from as well?

Who do they call, the FBI?

ROFL

Come on Renegade, you know who to call.  "The Gun Busters"

Stupid comment...dude, you have no clue what you're talking about.

OK so I'm stupid.  I do know the very first FFL I requested transfer info from (2010 or so) emailed me a list of his "rules".  One of which explained the NICS process and added that any denial would result in him calling the police.  In retrospect he probably threw that in to discourage prohibited persons from wasting his time but it was there nonetheless.  Wish I still had the email as I would gladly post it as proof.

Over the years I have seen reference to other FFL's doing the same on various gun-related forums, etc.

I NEVER SAID ALL FFL's DO THIS.  JUST RELATING MY EXPERIENCE.

Sheesh...