Get your figures right or your number is up in the den

This week's show was a bit of a downer, with a lot of interesting ideas which just failed to make the grade as business investments for the dragons. However, once again, the experience of the latest batch of entrepreneurs and inventors proved how important it is to know your turnover figures, profit margins and financial projections if you have any hope of securing investment.

Josephine Buchan brought a musical about Dusty Springfield into the Den with a stirring performance by singer Lucy Williamson of 'You Don't Have To Say You Love Me' to round off her pitch. Josephine seemed to have convinced the dragons that this was the right musical to launch at the right time, but then she hit problems. Firstly, the 'Fiercesome Five' couldn't get their heads around the quirkiness of theatrical financing; things then went downhill when Josephine couldn't answer straightforward questions about the costs of hiring a theatre; then - the nail in the coffin - Josephine's advocate, director Nickolas Grace, made the fatal mistake of saying: "Sometimes you have to make an investment for pleasure." By seeing the venture from his own point of view rather than the dragons' he sealed the project’s fate.

Emily Webb, an impressive young entrepreneur with an invention for rowers that originated out of a GCSE project, performed magnificently but was unable to persuade the panellist that there was a big enough market for her product. She also stumbled on her figures. What a shame. She had achieved a great deal, and it looked like a winning product.

In the programme's finale, Oliver and Toby Richmond secured £100,000 for 30% of Servicing Stop, their car servicing business. They were sure of their numbers and confident in each other's judgement. The duo offered a branded, fixed-price car servicing service through a network of 750 independent garages. This puzzled me – how were they going to ensure quality? The customer paid them directly, and they then paid the garage, so it looks to me like they could be liable if the work is done poorly.

There is an eBay-like customer feedback mechanism in place, but this only works after the event. If a car is poorly serviced, and this contributes to an accident, then the fact that the garage's feedback score is reduced in no way makes up for the possible financial and reputational damage. Though you may spend over an hour in the den being grilled by the dragons, a maximum of about 12 minutes is ever aired so maybe this point was covered off, but I’d love to know the answer!

Finally, a comment about Lawrence Webb and Frank Drewett who showed their wheelie bin Lid Lifter invention made from 'plastic and string' was far from rubbish. The pair illustrated that if you have a simple idea for a useful product backed by sound financials you are always going to be in with a chance of impressing the dragons.