Site seems fine to me - their store is close by to my home so I haven't placed an order through their website but have made purchases at their store. This is a legit company so I'm not sure why the poor ratings.
I have been to the actual store and this place actually DOES exist and is not a scam site. Addresses of real locations can be found here: http://www.partycity.ca/category/store+locations.do and I have not found any problems when visiting their site. Also http://hosts-file.net/default.asp?s=partycity.ca and http://www.google.com/safebrowsing/diagnostic?site=partycity.ca have not found any problems neither.
"Over the past 90 days, partycity.ca did not appear to function as an intermediary for the infection of any sites."
"Of the 37 pages we tested on the site over the past 90 days, 0 page(s) resulted in malicious software being downloaded and installed without user consent. The last time Google visited this site was on 2013-04-25, and suspicious content was never found on this site within the past 90 days."
If there were any problems in the past (previous to 90 days) I do not see any issues now (May 11th 2013).
Sobre este site
Canada's leading retailer of discount party supplies and Halloween costumes, with thousands of theme party supplies, birthday party supplies, and costumes and accessories.