"We'd recommend you purchase from authentic sellers and genuine retailers, and websites based in New Zealand.
"If you're purchasing from an individual, we suggest you request proof of ownership, or perhaps some form of ID.
"If the seller is not able to or refuses to provide these, it's possible the item may be stolen."
He added: "Generally speaking, if the deal is too good to be true, it often is."
Police say if you own a bike, ensure you record the serial number, keep a copy safe, and upload to www.snap.org.nz
If you purchase a bike, ensure you record these details as well.
Police say people should also consider a high-quality D-lock or similar to deter would-be thieves.