My attention was focused on the two customers in front of me when he walked in and sent the old string of bells at the door chiming.
Tighten this up; it’s not instantly obvious where our attention should be pointed, which isn’t okay in your first line. If “the two customers in front of me” aren’t crucial to the scene, I’d try using something else to convey the narrator’s distraction. Doesn’t have to be concrete. More importantly,–I shoulda said this first–you left the gate telling us something we’d like to observe and conclude for ourselves as readers. How can you show that she’s preoccupied by something?
After a brief glance at him Perfect place for a beat, a little physical action to punctuate the scene. No brief glances, ew. I turned my attention back to my two potential customers It’s cool to introduce them here; leave em out of the beginning, continuing my sales pitch about a cell phone and allowing my employee to greet the newcomer. The two humans across the counter from me were in their early twenties and retropunks by the look of it Tell us what they looked like, not the narrator’s judgment, which would explain what they were doing in my antique shop Wordy. The one on my right had a mop Cliché. Think of something fresher of lime green hair — cut short on the sides and long on top — that fell forward into her eyes as she bent her head over the phone, the myriad God I hate myriad. Everyone quit saying myriad of silver hoops traveling up her right earlobe gleaming in the shop lights. Too much action on the part of the earrings. Gleaming’s enough; let something with feet travel. The guy standing next to her had a long magenta ponytail pulled back with a strip of yellow leather, and each of his nails was painted a different fluorescent color. They both wore the tight bright clothing that was classic to their subculture. The guy even had on real denim pants.
These two last lines don’t jibe. It’s okay that we don’t understand who or what the narrator is quite yet, but be consistent. “Classic to their subculture” is a formal, scientific observation. “Even had on real denim pants” is a more normal reaction. It’s cool for the character to be capable of both, but give us a minute to meet her.
The ponytail pulled his hair back tightly Whoop! Whoop! Adverb to smite!, showing off the pointed tips of his ears which were a little too short and angular, a telltale sign of implants. I saw him glance I don’t hate glance as much as myriad, but it’s usually a pretty ickystupidboring way for a character to look at a thing several times at my own ears, and I could almost see his thoughts on his face What did his face do? as he tried to decide if my tips were real or if I just had a really good mod surgeon. Oo. Interesting. I want a mod surgeon and so will your audience.
So. All this description? It’s okay, but it stops the action cold, assuming the character we really care about is Door Chime Dude. If you’re into these “retropunks,” and I bet you are, make them pay for their presence, and do it in a way that doesn’t interrupt your story. I might write a scene with them, a conversation, to start off with, and Door Chime Dude can interrupt.
*This is all one super-long paragraph. Try breaking it up to make it less formidable, at least as a book opener.
I’d keep reading, but mostly out of curiosity. Needs a lot of rewriting. Better justify those ears.