Katie,
Usually it's the other way around where a donor wants a work to go into the collection but the quality/condition does not meet the criteria for accessioning. Our policy is that all gifts are "unrestricted" and let the committee make the decision if it is to be accessioned into the collection or used to generate income for the care or purchases of museum quality works. The committee should consider the recommendation by the curators/staff. We are up front with a donor and let them know the work may be accessioned or be sold to benefit the institution. (All this happens prior to any accessioning!) Just be transparent with the donor and the public and it should be fine. Hope that answers the question. (We wait 2 years after the gift to auction or sell especially after they are using the gift as tax deduction.)
PK