Opponents of the system between the Edinburgh Airport and York Place, which can carry up to 250 passengers per car, claim they have been running almost empty at times despite the recent festivals.
The city council is also being accused of a lack of transparency over passenger numbers, leading to further concern the £776 million project will continue to be propped up by the taxpayer.
Transport for Edinburgh, the arms-length firm that runs the service, said the 90,000 travellers each week meet their targets and that off-peak times, particularly at night, are expected to be quieter.
Now the critics are calling for figures to be made public about the number of concessionary fares and paying passengers, in order to assess the system's viability.
Alison Adamson, of Macphersons the Kiltmakers in Grosvenor Street, said local traders that had suffered from the tram works for years were still seeing no benefits.
She said: "Generally speaking there are very few people seen on the trams.
"I am one of the people that would like the council to issue the numbers of paying passengers, because the pensioners are subsidised.
"I don't grudge the pensioners the free travel but if you take that away, how many are actually paying to travel on the trams?
"I wouldn't recommend the trams because they are so unreliable."
Alan Rudland, director at Arkay Imaging in Leith Walk, added: "I think it is absolutely disgraceful that they are doing this.
"The details are obscured on the grounds of commercial sensitivity. It seems they are going to roll out any excuse.
"They have to be honest. It is a loss-making service that is being propped up by the council giving itself its own money then taking it back."
He added: "They claimed they were going to get concessionary fares grants from the government and they couldn't."
The cost of the trams increased significantly from the original £545 million budget, and the project dogged by other problems including a dispute with the track builders that halted work for months.
First Minister Alex Salmond launched an inquiry to find out why the project spiralled beyond its original budget and timetable after the service began in May.
The tram system has already been shut down twice, once when balloons became entangled in an overhead cable and again when a tram broke down at Haymarket.
Daniel Donaldson, a lawyer who set up a petition for a public inquiry into the trams, said the fares system had been "made deliberately over-complicated".
Lesley Hinds, transport convener and chairwoman of Transport for Edinburgh, said: "I've just got off a tram and it was standing room only.
"Of course there are quieter times on the tram just like there are on other modes of transport, and this is why there are peak and off-peak services.
"We're seeing patronage of 90,000 plus per week, which is in line with the business model, and we're happy with progress so far."
A spokesman for Edinburgh Trams insisted targets were being met, and added: "We're also happy with revenue performance at this stage although it's still very early days.
"As a commercial business owned by the City of Edinburgh Council, we have a responsibly to protect commercially sensitive financial information and report it exclusively to the council.
"We'll produce publicly available financial reports at the end of the financial year, but before that we can only release information to the council."