Bought a Lego City set for DS2 on Ebay, advertised as "complete" with instructions. Hot bidding war at the end, but with postage, probably still paid only about 1/2 the best possible new price (condition generally ok, but not like new).
Arrived missing about 9 pieces, contacted seller.
Got DS1 to list the bits with page numbers from instructions, sent verbal descrip with scanned in pgs. from building instructions to seller.
Seller took ages about a week to find & send the missing pieces (she said it was "all" of them). Two pieces are still missing, one we had a spare for, anyway, the other we neglected to tell her was missing (error on DS1's part).
I don't know whether to contact seller again. I know problems happen, but feel cheesed off that seller got it wrong twice. I wouldn't want to buy from this seller again, but it seems a bit much to actually Neg her for it in feedback.
I would email her and say 'look it's not as stated, I don't want to open a dispute but would not have paid so much if it was incomplete'. Then see if she offers to give you some of your money back. Which seems fair if it's not as stated.
If she makes a reasonable offer to you, give her positive feedback. If not, raise a dispute. I would never give negative feedback until I'd given the seller every opportunity to put it right.
I'm slightly cynical here - as I've had this situation and the seller said 'oh yes I'll send you the extras', some came, but not all and she didn't follow up to say sorry. So I did query it and she said 'Tough. I have done my bit, there are no more bits'. (Despite it being stated as complete) so I filed a paypal claim and said it was not as described and asked her to refund me the £3 it would cost to buy the missing bits on ebay. Ebay found in my favour and ordered her refund the full cost. I asked her if she wanted the whole thing back and she didn't reply.