So one of the tricky things to do is figure out how helpful is too helpful. Often times people don't like to be asked if they need help, but then customers might also complain that they were either ignored or couldn't get any help when they needed it. So you need to develop an eye for seeking or offering help.
-What I like to do is after greeting a customer, I go back to what I was doing and then after the customer has had the time to look around you offer them help. Give it a minimum of five minutes, but often times more is better. If a customer needs it right off the bat they will come to you, and you need to drop what you are doing (unless you were already helping a customer) because helping the customer does take precedence over all other jobs.
-Why the hell would you ignore a customer, even if you were in a bad mood? Seriously, customers equals business. No customer service equals no money and that equals no job for you. Your moodiness and anti-social qualities need to be tossed right out the window.
-If a customer looks suspicious, zoom in with an offer for help earlier than later. Sometimes you need to get a handle on people early otherwise they have too much time to case the store. If it looks like they are looking for something but can't find it and then they turn down your help, little mental red flags need to start going up. If they are twitchy they will hopefully get nervous that your paying attention to them and ideally drop the entire plan. If they aren't casing the place, then no damage done since you were just asking if they needed help.
-Don't keep asking the same customer if they need help. That's annoying. You should have other jobs to do. Go.
-Don't single out a customer if they are a woman. I've had guys crowd ladies and it's just embarrassing. Also, walking out onto the street and yelling at women to buy comics IS NOT ACCEPTABLE.
-Don't be afraid to ask for help. You need to measure the store staff as well, so nothing does that better than politely asking for help.
-Depending on the size of the store, the staff might be large enough that there are different specialties. Keep in kind that if you wish to get a handle on the store, you should also get a handle on the workers. While it would be nice if everyone knew everything about anything, that just won't be the case in general. Keep in mind we are just like you and we all have different tastes. I have one guy who specializes in Silver Age and Underground, one guy who likes just mainstream, a couple people who like a bit of everything, and so on and so on. Try to find the person who does the ordering, if you can. Ideally their brain should be some sort of nexus of comic reality since they have to know what the hell they are ordering.
-All stores order from the same distributor (Diamond), with additional smaller distributors to the side as well. If you want to find out if something is available, ask if it's available from Diamond. Any retailer should be able to look it up real quick like, and most of us will have the same access to items. There are slight differences depending on what coast you are on, and some retailers may have extra tricks up their sleeves. I just usually find it interesting when it seems some retailers won't place orders for customers and then I look up the same item and I do have access to it.
-Watch the clerk if he is already helping people and he is the only one around. Sometimes we have single shifts with no backup and then we get swarmed with a dozen people and the phone starts ringing. When you see an opening, by all means go ask for help. Just don't try to tackle us when we look like an aneurysm is imminent.
-If you come up to the counter and are ready to be helped and the clerk is somewhere else working (or even slacking off), don't be afraid to find us and say you are ready to go. You need to actually let us know if you are in a rush and not just assume we will magically pop up when your ready to go. If you are a customer I trust, I am probably not watching you like a hawk since I'm usually busy with other work.
-Parents, don't be afraid to ask if a comic is appropriate for children. If we intercept you because you are buying Johnny the Homicidal Maniac for a 6 year old, please just hear us out.
-Please please please have some sort of vague idea about what you need help on.
"I'm looking for a book. It's blue. People do stuff in it."
That is not acceptable. You think I'm joking. I am not.