Cash By Mail: the trade protocol
To remain safe with cash by mail transactions, there are a number of steps that Bob need to be take in order to ensure that there is no possibility of being scammed as explained by the following LocalMonero article:
Staying Safe With Cash by Mail (originally from LocalMonero)
If you're buying...
If you stick to high reputation sellers it's very unlikely that you'll encounter any issues while buying with cash by mail, however the following tips will help you prove your payment in a dispute should it arise. The most important thing to do is to make a video recording of your payment. Here are the guidelines:
Your video should be filmed within a single take, without cuts
You can put the cash in the envelope at home or in the car, and you can put your phone with the video turned on in your front shirt pocket and it'll record the whole process without much extra work from you apart from making sure that you do everything in front of where the camera's pointing. If you have something like a GoPro or the latest iPhone which has a camera with a wider viewing angle it's going to be even easier. Keep the footage in case of a dispute for 180 days.
Put custom markings inside the envelope
Use some sort of a custom chop/stamp/seal, or a signature or just random movements with a sharpie inside the envelope, covering all surfaces. This will help establish whether the seller is actually opening the envelope you've sent or a fake one. Make sure the mark is visible on the video.
Try to disguise the cash
To mitigate a (potential, but very rare) case of postal theft en route, try to conceal the fact that the package contains cash. You may put the cash in a magazine, mylar bag or some other container. Vacuum sealing the cash also works.
Place envelopes inside of envelopes
Instead of simply placing the cash into the envelope, use multiple nested envelopes for your package. Place the cash into the smallest envelope (or simply fold a bigger envelope as necessary), seal it, and place it into another envelope. Repeat this process until you have at least 3 nested envelopes. This helps ensure that if the receiving party tries to tamper with your package they will have a much harder time resealing it all in a way that would be undetectable when inspected by the dispute mediator.
Send with tracking
Packages sent without tracking may get lost with and without tracking it could be all but impossible to locate it. Having tracking also allows the receiving end to have peace of mind that the package is en route in case it's taking longer than expected.
Conclusion
As we've mentioned before, with established traders the risk for a buyer is very low. Very low doesn't mean zero though, so make sure to follow these rules to be prepared for a dispute situation.
And there are also a few steps that the monero seller (Alice) has to follow in order to make sure the trade is conducted in a secure manner:
If you're selling...
Make a video of receiving and opening the package
Record yourself receiving the package from the postal worker, the postal worker weighing it, record the label, all the outer sides of the package; open the package while filming with the camera pointed into it, run the cash through a counter and counterfeit scanner. Make sure everything is filmed in one take. Always keep the package in view of the camera. Keep the footage in case of a dispute for 180 days.
Under no circumstances finalize a trade early
The key thing to remember (and we put disclaimers about this on every step of the way) is to NEVER finalize a trade UNTIL you have the money and you are absolutely confident that everything is in order. A legitimate buyer won't pressure you into early finalize.
Have a buyer put a note with their username and trade ID
This will help you distinguish packages coming from different buyers and avoid confusion. This also will help in preventing man-in-the-middle attacks, where a scammer interposes themselves in-between the buyer and the seller, pretending to be the seller when talking to the buyer and pretending to be the buyer when talking to the seller.
To recap the recommendations we have the following graph:
Here bob puts the cash into a mylar bag (to disguise the cash), which gets put into a tamper proof bag (that way, if alice tries to open it, it'll be easy to see), then bob puts it into at least 3 envelope layers with custom markings inside each layer (again, as anti tampering measures), and then putting it inside the tracking envelope.
Also very important, Bob needs to record himself from the moment he wraps the cash into the mylar bag, all the way to when he places the letter in the letterbox. and Alice needs to do the same from her letterbox, all the way to unpacking the cash from the mylar bag. That way in case if there is a dispute, the arbitrator will be able to see who's at fault if there are any steps along the way that have not been respected.
In total per cash by mail transaction (assuming the final envelope weighs less than 100grams), the cost involved for the seller should be around 2 euros in France (including tracking), assuming the seller sends the envelope within the same country, and that he buys enevlopes, mylar bags and tamper proof bags in bulk.
