MM272;ALWAYS put limits on your buys & sells....I think the MM's have special 'sucker bin' for "Market Orders". Besides using your impending (tentatively committed) shares as you described they have number of other 'games' they play w/ Market Orders. They often will hold your MO 'buys' till the price is much higher and hold your 'sells' till the PPS is much lower...they have that option. They can also screw you royal by putting your trade thru when there is an outrageous 'spread' between buy/sell PPS's (especially in after-hours).
As one horrendous example of "Market Orders" gone bad; There was a company that was associated w/the huge Vanda 'pop' a few months ago. Their stock was trading at .05 on a Friday...the VANDA news 'popped' late that same Friday. Over the weekend, some newbie investors found out about this symbiotic company lurking in the shadows. Although people tried to warn them otherwise, many of these newbies put in M.O's for 100's of 1,000's of shates at .05
When the market opened on Monday, the opening PPS was $1.40+"each". Their MO buy orders went thru and a "lot" of folks went bankrupt, with no means or hope of ever being able to cover the cost (it even cost one guy his marriage). The PPS on that stock opened at $1.40+ , went to $1.70 w/in 5 minutes and back down to .69cents 10 minutes later. It is just now getting back to $1.70, 3 months later.
Moral of the story...ALWAYS use LIMITS
