I would also take it to a good small camera shop- they should be able to test the main functions for you free of charge (especially if they think you might sell it to them, and they'll offer you a crap price probably), but you can also get them to estimate what it's worth. Also check out ebay to see what similar cameras are going for, and seach around online for more info.
If you know nothing about it, state that in your ad, you're not mis-representing it that way. You might get a bit less money if it's sold 'as is', but people who are into this stuff know what to look for. If it's in good condition to start with then it's got more chance of selling.

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys