I think it’s a con. In the majority of episodes the participants keep within their budget but at the end of the day good old Simon O’Brien comes along and announces a list of additional costs. These include solicitor fees, estate agents fees but then a huge “interest on loan”!!! This latter cost is usually the killer blow to making any profit!!
What I would like to know is the “interest element” known to the participants prior to them starting work? I get the impression they are not.
If they did know I doubt some of the participants would tell the producers to stuff their show!!