Cabriolet Conversion - Beware
First and foremost, please check the chassis number!!! We can't stress this enough.
Cabriolet chassis number prefixes are as follows:
220SEb 111-023
250SE 111-023
280SE 111-025
280SE 3.5

111-027

A Mercedes Benz cut coupe transformed to a cabriolet - Be careful and know what you are buying!! This is probably the most informative photo of all. Notice how close the back gap of the trunk opening is to the chrome moulding around the top. A true convertible has a space of (approximately) 3 inches between the back gap of the trunk opening and the chrome moulding. Also the chrome moulding itself is 5 pieces on a convertible. (See closeup of next photo.)
Mercedes Benz W 111 coupe conversion differences soft top above the chrome moulding Notice in this photo that there is no clip. The chome moulding on a coupe is in 4 pieces. Another telltale sign is that the convertible top here sits above the chrome moulding, on a true convertible, the edge of the top tucks under the moulding.
Mercedes Benz W111 coupe conversion differences interior rear seat

On the interior there are also some differences in the rear of the car. Notice the seat in the next photo. It has the wider seat top of the coupe and not the narrower one of the true convertible. (This car didn't even have a headliner installed for the soft top.)

 
A TRUE Mercedes Benz W111 Cabriolet Notice in this photo of a TRUE convertible the difference in the rear seat area. This difference is to make room for the soft top with the boot cover when the top is down.
Mercedes Benz W111 coupe to cabriolet conversion soft top header panel In this photo of the header of the convertible top, is also a sign that this is a cut coupe.