newbie used bike fit/test ?

Hi all, I am new to this forum and triathalons and am on a quest for a bike.  I am looking at a used bike that has everything but the wheels (has shifters, derailers, breaks, etc...).  The guy selling the bike does not have any wheels to put on for me to test it out.  Are there any good ways to test fit, as well as funcanality of the components on a bike like this.  Thanks........vin