If you have a 30 amp RV, it can be a good idea to plug into 50 amps. A 30 amp receptacle in a pedestal can be in much worse shape since there are a lot more 30 than 50 amp RVs and 30 amp pedestals tend to be abused more. Perhaps the more important thing to know is that 50 amp pedestals have much heavier gauge wiring to them and they are less likely to have voltage drop issues. If you come across a pedestal with 30 & 50 amps, unless the pedestal looks fairly new and in good shape, I'd go straight for the 50 (with adapter).
If your RV is 50 amps, going down from 50 to 30 amps is okay too. Will only get 3600 watts of power max. tho. versus 12,000 watts but not usually a big deal if you do a little energy management.
In the US, the NEC requires only 20 percent of a CG to have 50 amps and 70 percent must be 30 amps.
ALL pedestals are required to have a 20 amp GFCI recept. regardless. As of the 2005 NEC edition, only 5 percent of sites had to be 50 amps. These are min. code requirements. Some CGs have been voluntarily built above min. requirements like some casinos, high end RV parks and some gov't CGs. You can have extreme difficulty in finding a 50 amp pedestal in a CG, esp. in the high season. RV manufacturers and dealers of course don't tell you how hard it can be to find 50 amp pedestals. The code in the US for RV parks has always waay better than in Canada and the last time I looked there was still nothing specific for RVs. The NEC tho. is still woefully behind on all the 50 amp RVs out there.
Older CGs can have no 20 and/or 50 amp recepts. The photo shows an older CG we were at once that had no 50 amps and any 20 amp recepts were removed. Clearly old with all the rust. (The 30 amp recept. was so loose I had to prop it up with a stick.) We carry a 30 to 30 amp pigtail for bad pedestals when there is no other option so that if the plug overheats and melts, only the pigtail will be damaged. CG owners often do their own electrical with unqualified staff and sometimes do things that don't meet code (and they don't often fix faulty wiring either).
Always make sure your plug blades are kept clean and shiny and do not plug in with the power turned on (will cause pitting on plug blades). The inside of pedestals can be in really bad shape but you can't tell from the outside. Regardless of having a 30 or 50 amp RV, it's a very good idea to at least have a voltmeter inside that is permanently mounted or plugged in and better still is get an EMS unit.