Zahir Qayum posed as a potential buyer wanting to test drive cars but once in the vehicles he forced sales reps to get out before driving away, once pointing a knife at one of the workers.
In March this year Qayum left the boot open of a Toyota Yaris he was viewing at Toyota World and, when the rep got out to shut it, he sped off.
However, a cup of water he had left on the roof flew off as he drove away and testing on the rim returned a DNA hit to the 41-year-old.
Officers seized clear CCTV images showing Qayum in the showroom and at three other dealerships where cars had been taken, as well as at an attempted robbery at a betting shop in the city.
In July last year Qayum was being taken for a test drive in a BMW, worth £17,800, from Listers Audi in Birmingham, when he pointed a four-inch flick knife at the stomach of the sale rep.
The victim pulled onto a car park and got out before Qayum moved into the driver's seat and sped away.
And a sales rep from Motorpoint Car Supermarket in Lichfield Road was taking Qayum for a test drive in a VW Golf GTD, valued at £18,999, in April when Qayum indicated he had a knife and threatened the rep before speeding off.
Also in April, Qayum threatened another sales rep during a test drive from Motofair in Sheldon before driving off in a Hyundai i30.
Three days later Qayum, armed with a syringe, grabbed a woman working at William Hill in Ward End, Birmingham and demanded cash. He eventually fled empty handed.
Following a four-day trial Qayum, of Maryland Avenue, Hodge Hill, was convicted of three counts of robbery and jailed for nine years at Birmingham Crown Court on November 7.
He was also found guilty of attempted robbery, theft of a motor vehicle, possession of a blade and four charges of driving while disqualified, with sentences to run concurrently.
Qayum was further disqualified from driving for seven and a half years.
Det Sgt Tom Lyons from West Midlands Police CID, said: "This prolific offender has used threats and a knife to intimidate his victims.
"A combination of strong forensics work and dedicated officers scouring hours of CCTV footage has resulted in him being convicted of 10 offences and sentenced to nine years in custody."