Abdi Mohamed, aged 26, was attacked by "delusional" Moses Smith outside Easy4insurance, in Upper High Street in Wednesbury town centre on June 8 last year.
Smith, of Brownhills, in Walsall, denied an offence of murder and has now pleaded guilty to the lesser charge of manslaughter on grounds of diminished responsibility.
Wolverhampton Crown Court heard that the Crown Prosecution Service has accepted his guilty plea.
After the hearing Mr Mohamed's family said they were unhappy with the outcome and believe the attack was racially motivated and have launched the Justice for Abdifaha campaign as a result.
In statement the family said: "Abdi had the most beautiful personality and no words can truly describe the person he was. He was a loving son, brother, cousin, uncle and friend.
"Abdi always had a smile on his face, an infectious laugh and always went above and beyond for people.
"The family would like to make it clear that they do not agree with the decision taken to accept the plea of manslaughter with diminished responsibility. Throughout this process, there has been a lack of transparency. Until very recently, we were preparing for a murder trial.
"We have seen the evidence which is used to argue that the defendant was suffering from a severe depressive episode at the time of the attack and it is not compelling."
Mr Abdi, who had limited contact with the defendant prior to the stabbing, was attacked after Smith went to the office to inquire about making a claim about scratches on his van. When the victim went to check the vehicle parked nearby Smith stabbed him multiple times in an incident which was captured by closed circuit cameras.
He suffered serious neck injuries, but died in hospital a short time later despite efforts to save him.
Paying tribute, a spokesman for Easy4insruance, where Mr Mohamed worked for two years, said: “Our thoughts are with his family in this difficult time.
“Abdi has been employed by Bromwich Insurance for two years as a Personal Insurance Advisor, he was in the process of progressing to Commercial Insurance Advisor such was his ability’s for learning.
“He was a very much loved member of our team and will be missed by us all for years to come.”
Smith, 38, of Lindon Road, Brownhills, will be sentenced in January and may face a hospital order.