Stephen Skehill wrote to Canberra Liberal Mark Parton on Thursday to advise him that because the commercials pre-dated his time in office, there was no issue with him appearing in them.

"The code of conduct for members of the assembly has no application to conduct undertaken by a member before they became a member," Mr Skehill wrote.

"In my view your actions in providing product endorsements for your clients in reliance upon your public recognition as a media personality and in preparing and appearing in such advertisements - the intellectual property in which would vest in the client upon completion - were simply normal and acceptable commercial behaviour of a type commonly undertaken by persons to whom the code has no application."

Mr Parton sought the advice of the ethics adviser after repeated questions about the appropriateness of a member of parliament spruiking one business on television, radio and social media ads.

The ads were made for Rolfe Honda before Mr Parton took office and he has no continuing financial arrangement with the dealership.

Chief Minister Andrew Barr had a crack at the dealership's marketing strategy, suggesting their sales would "plummet" given the "largest group of Canberrans" were Labor supporters.

In defending himself this week, Mr Parton likened himself to Midnight Oil frontman turned Labor minister Peter Garrett.

"When Peter Garrett was elected to the Federal Parliament radio stations continued to play Midnight Oil songs ... and the only difference there is that Peter would have continued to receive royalties from that airplay," Mr Parton write on Facebook.

Mr Skehill said while a member of the public might "entertain a suspicion" that the ads relied on Mr Parton's status as an elected representative to sell cars, as they were made before he took office "any such suspicion would be dumbfounded".

"Clearly there was no conflict of interest and no reasonable perception of such a conflict at the time you made the advertisements in question as you were not then a member," Mr Skehill said.

"Further if it is the case as you believe and as I expect that you have no residual rights over the subsequent use of the material you generated for your then clients, there is no action that you can now take that would necessarily resolve such a perception."

Mr Parton told Fairfax Media he was "completely satisfied" with the advice he'd received and hoped it put the matter to rest.