Not doing so or at least in a condescended form is kind of operating a fraudulent exchange. It is kosher to bundle 50 buy orders of 1 stock into 1 order or visa versa - get a bunch of little orders that adds up to a cheaper option. If it doesn't work out refund and inform that it failed to go through. If they asked for 1 share at $25 and you legitimately give it to them it isn't fraud. It is another to say "buy" Tesla shares for people when you really shovel it into another investment and work out what they owe when you think they will just go bankrupt and Theranos is the way of thw future....