I saw this refrigerant recovery thing on marketplace

That was designed in the 90's during the EPA phase-out and new regulations surrounding R12 and other refrigerants. As far as I know; these all had hermetic compressors. They would have used materials similar to all common compressors of the time period. The materials would never be able to withstand SO2 due to the corrosive nature.  These machines also contain specialized oil recovery traps, check valves etc. which would not be able to withstand SO2.  Everything in the system would rust and corrode. Also the desiccant filters could be a major compatibility issue with SO2 if they already contain trapped moisture which ends up reacting with the SO2

The markings on the machine for R12 are part of the EPA rules for how things had to be labeled; and not for any technically valid reason. The machine can be used to recover other Freon-type refrigerants as well; however it would ruin it to attempt to use it with SO2. 

There was one at a flea market which was too good of a deal to pass up. May have also been $40 or $50. I've been using it for an R152A recovery machine for several years. It works excellent for this. All I've had to do is fix a small electrical problem when I first got it; and replace the deteriorated hose between the tank and machine outlet. 

Having said all that, you can make your own recovery machine, without any moving parts. It will require a cheap deep freezer that you don't mind drilling a hole in. Place a standard refrigerant recovery tank in the deep freezer, with a hose connected to it.  Route the hose through the hole drilled in the freezer lid and connect it to the yellow hose (center) port on the gauge manifold. Connect your vacuum pump to the red (high) hose from the gauges.  Connect the blue hose to the hermetic service kit on the fridge (do not open the port yet).  Open red and blue valves on your gauge set and allow vacuum pump to remove all air from the refrigerant tank in the freezer, the gauge hoses, and the hermetic kit body.  Allow about an hour of time. Once it's evacuated, close the red valve to isolate the vacuum pump. Open the hermetic service kit to allow SO2 from the fridge to flow into the evacuated tank.  At this time, power on the freezer. Allow it ti sit like this until the SO2 transfers from the system into the tank. Once it's done, the tank will be in a vacuum again. 

Thanks to our member Gill (Coldspaces) for this method, by the way!  It can be used for virtually any refrigerant, too.

Sincerely,
David 

Just make sure to be careful when drilling a hole in the side of any fridge let alone a chest freezer. Chest freezers normally have the condenser coil running between the inner and outer walls.