Customer 55 (asshole)

Customer came into the store one day and i made her an offer. $240 worth in accessories for her phone for less then $15 and saved her $20 per month on her bill keeping the same coverage she has now. Its a steal to say the least so she takes it and comes back 4 days later to return it. So i'm just starting training for a potential promotion and 5 min into training i'm called out to deal with her, i work with her for 3 min and all she can do is yell and complain on how customer service said this customer service said that blah blah blah and i'm like.... ok? She demands to return her Bluetooth headphones, speaker, and battery pack that she paid less then $15 for and to go back to her old pricing so she can go leave and i'm thinking... you brought me out of a potential promotion training for this? So i get back to training only gone for a few min and they are still making sure the headset and microphones are working so it hasn't started yet. The trainer calls my DM who calls my manager to tell me not to step away again. Now i'm pissed because this woman has played with my commission and played with my potential promotion. She was even told i was in training and her reply was tell them they will have to wait. Needless to say she will not longer be helped by me as i offer to save her money and all she did was waste my time.