How do I avoid using the same URLs in scrapebox?



I assume you mean over long periods of time...

After each posting run, do a link check. Save all found links out. When you have a new list or are hitting an old one, load it into the harvester, then do the import -> compare lists function and load up all your found links lists. The left over urls are the ones you've never hit before.
 
Scrapebox? Line check? Harvester? import -> compare lists? Are there any other newbies besides me who have no idea what the hell all that is about?
 
Select URL List to Compare, then select a list you have commented on already, those URL's will be removed from your freshly harvested list leaving you with unique URL's.

You can also select URL list to compare on a domain level so you can avoid posting on the same domain completely rather than just the same URL the choice is yours.