Patent Publication Scams
Many countries publish patent applications 18 months from the date the application is filed. Scams have arisen based on the information published at this time which offer, typically, to register your application. Normally the offer is posted to the street address shown on the application, and it will look very attractive.
Careful reading will show that at best the offer is to register your data in their virtually unknown database. You can safely ignore such offers - all valid correspondence goes to your representative.
Patent/trademark Renewal Scams
Some time before a patent or trademark is due for renewal you may receive a posted offer to renew the registration. At best the price is usually exorbitant, at worst this may be a pure scam. Either deal directly with the Patent Office concerned or use a known qualified firm.
Domain Name scams
If you own a domain name in some country - "xyz.co.nz" - you may receive a notice from an organisation you have never heard of advising you that a second organisation you have never heard of has taken a list of similar domain names - "xyz.cn; xyz.tw; xyz.hk" and offering to take action against them for you. Resist this offer. A little investigation shows that both organisations have the same owner and that the countries in which the domain names are registered provide ridiculously cheap domain name registration.
Cheap Patent Applications
Offers to file your application for really low fees imply that there is no checking process, and you might as well be filing directly with the Patent Office yourself. You pay for expertise in providing content which will give a firm basis for a patent and for providing it in a form which will work worldwide. If your attorney asks no technical questions either your briefing is perfect or the end result is suspect.