He was convicted of fraud yesterday after an investigation by trading standards officers proved that he bought the goods from Sports Direct and signed them himself using a permanent marker pen.
Rennie, 46, of Banbury, Oxfordshire, was warned by a judge that he faces a substantial prison sentence. Former Manchester United star Rooney helped the prosecution by proving his signature on one item had been copied after officials from Dorset Trading Standards made a test purchase of a shirt for £150.
Rennie was found guilty after a four-day trial at Bournemouth Crown Court. His estranged wife Clare, 45, had previously pleaded guilty to her part in the scam and is also awaiting sentence.
Rennie claimed he had a team who spent hours outside football training grounds waiting for stars such as Rooney, Ronaldo and Lionel Messi to sign goods.
After receiving complaints about his company, FA Premier Signings, trading standards officers launched an eightmonth investigation and found he had conned 4,500 victims over nine years.
They included a mother who paid £300 for a Thierry Henry shirt to cheer up her son after his father died and a woman who paid £280 for a football “signed” by 23 Liverpool players for her husband’s 40th birthday.
The court heard Rennie sold 200 items supposedly signed by Messi, 272 by Ronaldo, 335 by Gerrard and 220 by Rooney.
He supplied a “certificate of authenticity” but the prosecution said this was also fake. When officers raided his home they found a stack of unsigned shirts, footballs and boots, as well as blank certificates and permanent markers. Rennie did not pay tax on the cash he made and spent some of it on family holidays to Florida, on one occasion taking £10,000 spending money.
Neil Martin, who led the trading standards team, said: “A successful investigation like this can only happen with the backing of evidence from those affected.
“This includes consumers, legitimate businesses and in this case Wayne Rooney, who initially confirmed that a signed shirt we purchased was a fake.”
Judge Peter Crabtree told Rennie: “You have been convicted of extremely serious offences. The sentence is inevitably going to be a custodial one.”
Rennie, who is now working as a postman, was granted bail and will be sentenced next month.