LYNN – Unhappy with the purchase of a stereo system from the back of another man?s truck, a Lynn man allegedly threatened the seller with a knife on Saturday after the two haggled over the price.The suspect, Alvin Antonio Bernardez, 20, of 55 Collins St., was arraigned Monday at Lynn District Court by Judge Albert Conlon on charges of armed robbery, trespassing, disorderly conduct, malicious defacement of property, fence.He was ordered held in lieu of $500 cash bail with a probable cause hearing scheduled for April 5.According to court documents, a 29-year-old victim reported to police that he was being robbed by two men armed with knives in the area of Northern Avenue and Relay Street Saturday afternoon. Police chased a suspect, later identified as Bernardez, as he ran up Relay Street and jumped over a picket fence, snapping two pieces of it off. After being pursued on foot and then by a police cruiser, Bernardez eventually stopped and was arrested.The victim later told police that he had been driving around on Relay Street with a passenger, when he was approached by two Hispanic males who accused him of ripping them off from a prior sale. Bernardez and the other suspect, who has not been arrested, allegedly had knives on them and made the victim open the doors to the van. After allegedly taking $20 in cash from the victim?s pockets, the two suspects ran away when they heard sirens in the distance.Bernardez told a different story during his booking, saying he had met the victim on March 4 and agreed to meet the next day so that he could buy a stereo system. He said he didn?t know the other Hispanic man at the scene, only saying he was another unhappy customer. For his protection, Bernardez said he brought a knife with him and handed over $200 for the system. The victim and Bernardez then haggled over the price after the victim said he wanted $300 instead.After a few minutes, Bernardez said, the victim closed the sliding door of the van, so he pulled out his knife and demanded his money back. At that point, the van started to pull away, but he said he noticed that the rear door was still open. He then reached in and pulled out the stereo that he paid for. After hearing sirens, he said he began to run away and threw the knife in a nearby yard.