Colum

no, this is perfectly fine. if the bid were 40, ask 42, you could place an order to sell at 41.5 and the bid/offer would go to 41.5 x 42 (assuming you have a round lot order). however, a market maker in receiving your order couldn't print an order for itself at 41.75 and then print you at 41.5. your order if it's inside bid/ask takes precedence over the market maker order. in NASD they created a rule to protect customer orders called the manning rule that is pretty much just this... a market maker can't front run a client order. to tighten up a spread (but not necessarily print anything to the tape), either a client or a market maker could post up an order to narrow the spread. they then become the inside market.

so in your case, you narrow the spread to 41.5 x 42... you want to buy, but chances are if anything you may get your order off on the sell side. granted, if you wanted to buy 20k shrs and you placed a limit for 100 shares to sell in this day and age where a lot of orders will follow bids/offers, who knows... maybe you could do yourself a favor, but you probably would be better off placing the buy order at 41.5 or 41 limit and see if your order gets filled than go other side of what you're intending to do.