As a general rule, one should always take seriously the receipt of a cease and desist letter that claims you are infringing a patent. A patent pending application does not give one the right to sue for patent infringement. Only an issued patent gives one the right to sue for patent infringement.
CAN YOU AVOID PATENT INFRINGEMENT UNDER THE CURRENT SCOPE OF PATENT CLAIMS IN A PENDING PATENT APPLICATION?
A utility patent application is filed with one or more claims. After the application is filed, the patent office may issue an office action that rejects one or more of the claims. The reasons for rejection can be many.
patent infringement for past damage goes back six years
US patent only prevents infringement in the US. If you make the US patented product in a foreign country and do not export the product into the US, there is no US patent infringement.
might be best to first file a provisional application before disclosing the invention to the manufacturer. But even if you do, the manufacturer can still steal the idea and you would not be able to sue for patent infringement with a provisional application
Design infringement occurs when the allegedly infringing device is substantially the same as the design patent, when viewed by an ordinary observer. Unfortunately, the infringement test is not based on an amount of difference (e.g., slight).