Your point about the CCTV is the main fact that makes the drug deal angle an unlikely one, more than anything else. I don't actually remember if it was confirmed the CCTV is from the Shell though, I thought someone said it was actually from across the street. @cedgison can you confirm that for us? What we do know, based on the still images, is it was terrible quality - I really don't know how they could discern who was who or what car was what with that footage. While someone else's phone or a phone we don't know about could have been used, you are correct that LE not only probably knows who car 3 is if they are known to Danni, but they have her phone and should also have her ping info and records by now.
Of course, there is SM discussion about a phone call she did make to someone that night which fuels the drug angle but I do prefer to work the more obvious angles until we can say for certain they are impossible.
I've wondered the same thing- if the footage was so terrible, how could they be certain which car belonged to each person? Just because I don't think there's enough evidence to completely rule out a drug-related occurrence, could Car 1 have been a dealer, Car 2 have been DW/DNV and Car 3 have been the other? JUST BRAINSTORMING If DNV set up the deal- which I think people go to because, well, we assume she knew people based on her people circle- and realized she left her phone, maybe she signaled DW not just to say she lost her phone, but to also let him know this is where we're going?
Admittedly, I don't think this is likely since both cars got there at 11:05, but sometimes brainstorming on other ideas does help rule out things.