Actually caught up the the GM '04 owner here at the port and he's been using Marshalls Bury St.Edmunds for the last four years.
He's never had an issue with them and they have always seen him right.
He also told me that the majority of staff and mechanics there used to work for the previous franchise holder, Jeffries Nissan.
He told me that when Jeffries were the franchise holder, it was more of a family run business, with many staff and mechanics being from the family.
When Marshalls took over, most of them remained and they are keen to keep the standard of service at a high level.
They know that if they didn't, many regular customers that were used to the Jeffries high standard, would take their business elsewhere.
Hope this helps.