I have had similar instances where some pedestals had corrosion, wiring issues, water intrusion, etc. at the campground. I do the same thing David and Dayle do. I carry a circuit tester, 30 amp and 50 amp adapters in my RV setup kit. This way I can test the pedestal before hooking up my rig to it. Circuit analyzers/monitors are good too to protect rig from surges and frequency changes that could upset some electronic components.
As far as 50 amp vs. 30 amp pedestals. To be absolutely confident that damage won't be incurred using the 50 amp pedestal on your 30 amp rig you should know the construction of the electrical system. I have a 30 amp rig. There are 2 40 amp fuses in my power panel to protect from surges. Amps is the flow of electricity, so when flow increases, so does heat and that is what melts the fuse and breaks the contact. The wire size plays a part in this...the smaller the diameter of the wire the more heat can be produces because of increased resistance. Take a look at some basic electricity you tube videos to help understand. I am an aviation mechanic who works on electrical systems and not a certified licensed home electrician--FYI.