After building up their career in professions ranging from doctors to accountants, many self-employed taxpayers decide to change tack and operate as a company, attracted by the tax treatment of the initial transaction and subsequent income. But a dispute with Revenue has now put key elements of this model into question.  A GP was before the Tax Appeals Commission recently, facing accusations of having underpaid his income tax by some €95,000. Compared to some, that’s not a big number, but the significance of the 138-page judgment in the case lies in TAC’s consideration of some tax issues arising from the…