facebook rookie

i only joined facebook when Love of My Life and i carved out enough money in the monthly budget to get internet service at the house. this happened last august. (we have been working very hard since sept 05 to get out of the bondage of debt. internet and cable have never been a priority. the rabbit ears work just fine...anyway, we're almost there, and internet is quite a luxury to have.) all that to say, i still consider myself pretty new to the whole facebook thing. and that is cause for some questions.

my friend lindsay has written a few things on the topic of facebook etiquette. however, i still have one measly question:

WHAT DO I DO WHEN SOMEONE I DON'T THINK I KNOW ASKS ME TO BE THEIR FRIEND???

i don't want to just "ignore" them...what if i'm supposed to know them? what if they've gotten married and the last name doesn't sound right and their profile picture is too small to see? i don't want to hurt their feelings (please note: i don't mind rejecting an invitation to some "save the squirrel with three legs" cause...i have an animal activist friend that i've known since 5th grade. she sends a save-this-animal invite about every week and i'm over worrying about hurting her feelings for not accepting.) but at the same time, i don't want to accept their invitation if they are a stranger. that's where there are problems. i have about 5 of such people waiting for my "friendship confirmation." any ideas on what to do here? help a girl out.