Let's say that an investor owns $100,000 of a mutual fund and he decides to sell. This order would be settled at the market's close.
Can the mutual fund refuse to execute the sell order, perhaps because it's more beneficial for them to continue to hold the assets?
Yes, a mutual fund can refuse to execute a sell order (more correctly called a redemption order) under certain circumstances. These circumstances must be described in the prospectus that the fund provided to you when you first tried to invest in the fund and which prospectus you acknowledged that you had read in order for the fund to accept your investment. Ditto for all later investments too.
So, what are typical reasons for such refusals? Well, some funds don't like frequent trading and so restrict redemptions for some period (e.g. 30 days) following investments. Or they might allow redemptions within the prohibited time window but charge an x% fee on such early redemptions. Other funds have rules regarding large redemptions (and I have no idea whether $100K is considered a large redemption or not) that say that large redemptions will require n days to process. Most mutual funds have a ready-cash account into which incoming investment money is deposited until it can be invested into securities and from which small redemptions are paid out immediately, but for large redemptions, the fund may need time to sell securities so that it has enough cash on hand to pay out to you, and so they allow themselves n days to process your redemption order. In some cases, they may do a partial redemption that very evening and process the rest in a few days.
