Even if they had tapes of him during a buy without being caught in the act of buying, selling or in possesion it means nothing.
You're misinformed. The fourth amendment has been severely eroded by the war on drugs. Here's an article on a recent example where 38 people were imprisoned based solely on the testimony of one corrupt undercover cop (no other evidence).
http://news.mysanantonio.com/story.cfm?xla=saen&xlb=180&xlc=1070131
Excerpt: Forty-six people, 39 of them black, were arrested in the 1999 cocaine sting in the small Panhandle town of Tulia, a farming community near Amarillo.
Thirty-eight defendants were convicted and imprisoned based on what Blackburn contends was fabricated testimony by undercover agent Tom Coleman.
"There was absolutely no evidence to back up (Coleman's) accusations," said Blackburn, who fought, along with the ACLU, to have the convictions overturned or the cases dismissed.
A major break in unraveling the state's case came while White was awaiting trial. Twelve days before the trial, she was offered probation in exchange for a plea, but she refused, Blackburn said.
The next day, a bank in Oklahoma, where White lived at the time, found a record showing she was in the lobby depositing a check around the time Coleman claimed she was selling drugs in Tulia, Blackburn said.
White deposited a $168 check and took $8 of it in cash. "That $8 saved her life," Blackburn said.
Though White's charge was dismissed, three of her siblings served a combined eight years and 22 months in prison before being pardoned.