Scalping around the stadium has gone down and is overpriced since the NFL allows season ticket holders to officially sell tickets via NFL ticket exchange. The only time I would recommend scalpers is if the game is sold out and no tickets (or very few) are available on the secondary market.
Since we really suck so far there is some good prices on the NFL Ticket exchange (Ticketmaster). I just put two tickets up myself for face value ($80 each) in section 347 (30/40 yardline, home side) for the next game. The people who were supposed to go bailed out.
Like I said: scalping is old fashion especially since the Dolphins have an electronic ticket system. You literally can buy tickets in front of the stadium online via your cell phone and have those tickets scanned at the gate on your cell phone.
If you ever look for tickets this should be your search in order:
1) Ticketmaster (most available since season ticket holders post there)
2) Stubhub
3) any other reputable secondary market website
4) scalping
Ticketmaster has one more advantage: most tickets offered on resale are season tickets. If you buy those you get 10% off on all items (including food and drinks) in the stadium. That is a season ticket holder benefit and stays with the ticket. Any blue dot seats are venue (Dolphins) - no 10% off. Any other seat is resale and has 10% off inside the stadium.
If you still want to try scalpers your best shot is at the Turnpike Exit in Miramar/Miami Gardens. I believe it is Exit 47. If you tell me where you are coming from I can tell you how to get there.
If you are nifty in negotiations and if you have a few minutes you can load the ticketmaster page, you can drive up to a scalper, ask him for a price and then compare it with ticketmaster on the spot. If he/she is higher try to negotiate him down. But be aware that a purchase through a scalper does not guarantee you tickets. Fake tickets are a possibility.
I hope that helped a little.
P4E
PS Most tickets placed through the NFL ticket exchange expire at the start of the even. Some listings do expire 1 hour before the event.