Keep the deal, mark as expired, and link to the original deal. That way everyone benefits - and people who missed the original deal then can rep the "spammer" for bringing the deal to their attention, whilst adding heat to the original deal. Isn't that what this site is all about - sharing hot deals?? As it currently stands, you get labelled a spammer and lots of people get put off posting deals again - not me 'cos I'm thick skinned ;-)
If you need some more space on the interweb thingy, delete inactive grocery deals from 1 / 2 years ago
Actually if there was a secret 3rd option "expire as duplicate" you could then safely delete all these after a period of say, 3 months.............