mommyof1
What type infant seat did you have and what kind of car do you have?
Most carseat manufacturers and most vehicle manufacturers will NOT allow you to use the two outboard anchors to form a latch position in the center. Even if the seat manufacturer allowed you to use the seat in this way, you must have the vehicle manufacturer agree. This means, basically, that latch can be RARELY used correctly in the center seating position.
I have a copy of the most current LATCH manual (put out by Safe Ride News, a very well respected resource in the CPS world) that summarizes (among other things) what each vehicle and car seat manufacturer say about using latch in the middle seating position.
LATCH comes from federal legislation. It is far from perfect. The federal law requires two latch positions in most cars. They are typically, but not always, behind the driver and passenger seats and not in the middle. LATCH works by having the LATCH anchors a specific distance apart. Most LATCH anchors (if you are incorrectly using the outboard anchors to form a middle position) in the middle are NOT this very specific distance apart. That's why it doesn't work.
The middle rear seating position is a great location to install a carseat. It is the farthest point from any impact in a crash. However, LATCH does not exist in most middle seating positions. Remember, LATCH is designed to make installation EASIER. It is not any SAFER than using a seatbelt. So if you want to install a car seat in the middle position, you generally have to use the seat belt to do it.
Good luck.
ETA TO ADD: I'm sorry I forgot you already mentioned you have a Mercedes and VW. Neither VW nor Mercedes allow you to form a middle LATCH position from the inside anchors of the two outboard positions. I'm not just guessing here. I have looked both up in the LATCH which is pretty much the gold standard for techs and instructors to use in the field! Even if your vehicle owner's manual does not say you can't use LATCH in middle, that doesn't mean you can. You must find an affirmative statement in the manual stating that you may use Latch there.