roberto clemente topps card

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at my parents house i have found a collection of many sports cards. There are quite a few of them with age. 1950's -70's for the baseball cards. And there is a slew of basketball, football, and racing too but they are more recent1980-90's. the problem is that there are so many and they are all mixed up in some desk drawers and i have for the most part found most of the 1970's baseball cards and as i look thru completed listings on ebay the prices seem to vary. for example i have the roberto clemente #50 1973 card here in front of me and i looked it up on ebay and it seems to be a valuable card but none of our cards have ever been graded. the roberto card is in a plastic case and appears to be in what i consider ex condition but how do i know? unfortunately some of the other cards i have already taken to my house and dont have them here in front of me. I just would like to get to the bottom of my researching and not waste time guessing. also who do you recommend me me discussing basketball, football and racing to? it would take days to sort thru all of these cards. Is it worth the effort to do so? The dozen of 1970 baseball cards i have in front of me here showed no search info. on ebay so i dont have a clue as to compare it to some of the ones that i did find on completed listings on ebay. Any help would be appreciated. thanks torri in VA