Decisions made by art museums about what objects to acquire and what to exhibit affect the prices that those works of art and others related to them can command in the market. In the case of “related” works of art, the mechanics are very straightforward: if the Museum of Modern Art, New York (MoMA) buys a Lawrence Weiner painting, then that’s good news if you happen to own one. And the more closely related your painting is to the MoMA’s, then the better news it is – most obviously, if it is painted during the same period; of the same quality; in the same medium; and the same size or bigger – the greater the impact of MoMA’s decision to acquire it will be on the price of your work. All other things being equal – which, of course, they rarely are – the greater the standing of the museum, then the greater the impact of its actions on the value of affected works. So MoMA moves markets, so to speak.

This is one obvious reason why museums need, axiomatically, to be able to make decisions about acquisitions, whether bought or donated, and about the choice of works to borrow and display, free from pressure from third parties who may stand to gain from any increase in their value or the value of related works.

Obviously, there may be difficulties when those third parties are also responsible for the governance of the museum itself: that is, when they are also first parties. Museum boards are unsurprisingly filled with collectors who should, and usually do, formally recuse themselves from decisions that are likely to have an impact on the value of works that they own; most obviously, the decision to seek to borrow and display a work for a specific show, or the decision to acquire or de-accession works that have a relationship to their own holdings.

Professional codes of ethics of most national self-regulatory bodies in the art museum sector and of the International Council for Museums codify this elementary economic logic. And it is the responsibility of museum boards and museum directors to ensure that these codes are respected, which they generally are. When disrespected, they turn a museum into a pump for parlaying public standing into private gain and they systematically reduce the standing of the museum in the process.

This is all pretty much black and white: the integrity of the art museum sector, as is always the case with self-regulated systems, depends on the clear articulation of the ground rules; on the probity of the players; and on the transparency of decision making – in this case by curators, directors and board members.

There are however some grey areas, and two are dark grey. First, should museum staff be free to advise board members (or other collectors) on what they should be acquiring themselves, and should those board members who are also active collectors be free to acquire works informed, in effect, by the insider knowledge that they are making the same bets or judgments as the museum on whose board they serve?

There is no such thing as a one-handed economist. On the one hand, it’s the excitement of the studio tour, of meeting the artist or, if deceased, at least their biographer or widow(er), and of participating in the carefully staged debate of the acquisition committee, that makes the tedium and the cost of serving on a museum board worthwhile. Why on earth can’t you show your conviction by supporting the artist directly as well as through contributions to the museum? Indeed, it’s often the board members’ enthusiasms as collectors that draw them close to the museum emotionally and financially. Collectors make passionate, informed and often generous trustees. And that is better than the alternative.

On the other hand, insider trading is not a victimless crime, even if the art heist perpetrator is, in this case, barely conscious of the crime committed and would be wildly dismissive of its seriousness if confronted. In the highly subjective world of contemporary art, in particular, reputations are made by a relatively small group of movers and shakers – critics, dealers, collectors, and curators – and the collector may be as influential, or more, as the curator in the mix. But in so far as the museum authenticates and ratifies the collectors’ judgement, and the collector is ahead of the market in their acquisitions as a result of their board service, there is an outstanding and knotty issue in museum ethics.

Second, art museums tend to object when a work on loan is “sold off their walls”. And when the whole exhibition is sold off they are seriously upset. Collectors benefit from a loan to a museum when the work’s value is enhanced and the loaned work is subsequently sold at a higher price than would have been possible without the provenance and public relations boost that the exhibition loan furnishes. This was one of several transgressions of which Charles Saatchi stood accused in the “Sensation” brouhaha – he sold many of the iconic works in that exhibition in the years following at prices significantly increased by the publicity they received when exhibited at the Royal Academy in London and the Brooklyn Museum of Art in New York.

This is also the fate of Alan and Simone Hartman’s collection of Chinese Jades displayed at the Boston Museum of Art in 2003-04 and subsequently sold at auction and, most recently, of the contemporary Chinese collection acquired for auction by the dealer Bill Acquavella after exhibitions at the Louisiana Museum in Denmark and the Israel Museum in Jerusalem (pp1,4). And I predict that there will be a continuing series of disposals of prominent and recently built collections over the next few years as unstable economic fortunes founder and weakly-grounded tastes change.

In these cases, museums serve as accomplices, albeit unwilling, to a sequence of events in which their standing is appropriated for private gain. The lenders who subsequently dispose of their loans may have had this intention all along or their circumstances may simply have altered – force majeure. But museums, in protecting the public interest and their long term reputations, have a responsibility to seek and secure firmer assurances about intentions than they currently do – and not to be (or appear to be) suckered by lenders. This is particularly so in cases where one is not talking about a single work but an entire exhibition or display of related objects, shown and catalogued as an entity, then broken up and sold off following its display. A nuanced code of ethics is unnecessary and no substitute for a measured and objective judgement of probabilities. To quote Nancy Reagan: “Just say no.”