Smith isn't one of M15's new recruits but is a mystery shopper.
"I suppose that on occasion I could be described as the customer from hell," he says. "It's my task to ask awkward questions and gauge the staff's reactions. At other times I merely observe and to all intents and purposes I'm just a normal shopper."
Mystery shopping and its associate, mystery travelling, is one of Britain's growth industries and is estimated to be worth pounds 40m a year.
It started in the US where it was initially used to measure the width of the smiles and the sincerity of the "have a nice day" sign-off used by staff in fast food joints.
However, it is now a much more sophisticated business. In the UK mystery shopping is used by retailers such as Dixons and Sainsbury's as well as by other sectors such as airlines, pubs and hotels, to identify and if necessary to improve, levels of customer service.
And it is not just about retailers spying on their employees, mystery shopping organisations say. The Association of Market Survey Organisations, which represents a number of mystery shopping companies, says: "Mystery shopping is now a much more considered tool and is now used by almost any business where service is delivered."
Mystery shopping is just one in an armoury of weapons used by retailers to fight bad service. For years British retailing has been associated with surly or incompetent staff more interested in discussing their plans for the weekend with their colleagues than in helping the customer. That image, coupled with low pay and long hours, has not made retailing a career of choice for graduates. "But if service improves, through initiatives such as mystery shopping, then retailers attract a higher calibre of candidates and things improve. It's an upwards spiral," Smith says.
Some of the mystery shoppers themselves are graduates and full time professional market researchers such as Smith, who has ambitions to move further up the career ladder in the research industry. Others are authentic amateurs who undertake their assigned tasks part time in return for a fee usually between pounds 12 and pounds 15 for a 15-minute shop - or in the case of mystery travellers, for the chance to stay at a hotel and eat dinner free and receive some expenses.
Alan Holliday, managing director of BDI, which claims to be the UK market leader in mystery shopping, says: "We don't use actors. We employ real people who are used to the situation we are asking them to investigate. If for example we are looking at Virgin's Upper Class service then we use real business people to test it out. Similarly if we are investigating a chain of bookmakers we use real life punters."
But fans of "Ab fab" should beware - potential Edina and Patsy's will be disappointed. Mystery shopping is not a job for shopaholics or those prone to histrionics.
"It's not a case of swanning off to your favourite department store for hours of browsing or pretending to have a temper tantrum," Smith says.
Mystery shoppers, having been given a full course of training, work to a tight brief. Their tasks can include observing the length of queues at a supermarket delicatessen counter or counting the number of tills open to asking complex questions about a camcorder in an electrical retail store. Their findings are either sent to the shopping organisation or phoned in and for analysis. The client can if necessary receive a report within 24 hours and set about putting any problems right.
Holliday says that mystery shopping allows clients to identify potential problems quickly. "Although the British are beginning to complain more about bad service, they are much more likely to vote with their feet and take their business elsewhere. We try to prevent that happening."
Although levels of customer service may be rising, mystery shoppers will not necessarily be out of a job. If the expectations of consumers increase then the satisfaction levels must increase still further, he says.