RE:RE:RE:RE:RE:RE:RE:RE:RE:007Using Level 2 as a guide - you can see the upcoming bids and asks. 
Using THC BioMed as the example (Real-Time)
Trading at: $1.41
Highest Level 2 Ask - $1.45
Lowest Level 2 Bid - $1.35
Now if an investor throws an ask for $1.35 - order is filled. Why they would, back to the STOP LOSS order.
Can 2 traders potentially collude, in theory, Yes but it;s a zero sum game - if I buy below market I gain a few pennies but you sold below market so you lost a few pennies so together we haven't accomplished (or gained) anything.
And I would assume that any continuous back and forth in any material amounts would set-off a flag.