Their claim stems from the reports of guns flowing south across the border via things like straw buys, which are a lot harder to detect than some would like to believe. However, their latest claim is just bonkers.

You see, Mexican officials think that part of the problem is "online shops" and the United States Postal Service.

The case of a man arrested in Texas, in the south of the United States, for shipping arms parts to Mexico immediately caught the attention of authorities in both countries. But it was only one thread in a web that continues to become more and more tangled.

At a binational meeting in early October, following the inauguration of leftist President Claudia Sheinbaum on 1 October, Mexicans complained to their counterparts about the flow of gun parts through online shops and the United States postal service into Mexico.

The host, the Mexican government, briefed the United States government on the issue and asked for more measures to control the smuggling, including uniform shipping codes to make it easier to identify packages and confiscate them, which Washington has so far rejected.

First, let's keep in mind that a lot of gun parts fall under export control laws, which means most "online shops" aren't shipping to Mexico. In fact, most won't even on non-controlled parts simply because they don't want to have to deal with the hassle of keeping track of which parts are covered and which aren't. It's just easier to not export any.

And, to some degree, Shienbaum seemingly agrees.

Sheinbaum herself stressed in her morning conference on Thursday 9 January the importance of cooperation to curb trafficking at customs and borders.

“Just as they are concerned about the entry of drugs into the United States from Mexican territory, we are concerned about the entry of weapons. What we are very interested in is that (with Trump) the entry of weapons stops,” she said.

Mexican drug cartels hire individuals in the United States to ship parts to Mexico, where they assemble the weapons, and people who receive payment in cash or remittances on both sides of the border.

So are these shops are just regular people buying parts and shipping them south.

My guess is that it's the latter, in part because of what I said before about actual stores not being big on violating export restrictions. Private parties who knowingly ship to the cartels, however, don't care.

That's not an "online shop" or anything of the sort, though, at least with regard to what most people assume when they hear such a thing. 

Any proposed fix is going to be a problem as it currently stands. Further, the idea of "uniform shipping codes" is an alarming proposition.

We already have a problem with gun-related items getting stolen via the postal service. Package theft is already an issue as it is, but if you start putting a particular code on packages containing gun parts, it's only going to get worse.

And it wouldn't actually address the problem since it seems the problem is private parties and not companies.

I can tell the USPS that I'm shipping just about anything and unless they're given a particular reason to doubt my word, they're going to assume I'm telling the truth. They kind of have to since they can't look inside of the box.

That means I can send an M240 into Mexico and tell them it's a machine part and the USPS has no way of knowing otherwise without examining the contents via some means and considering how many packages they get every day, an x-ray or something like that isn't practical. Shipping codes, though, will do even less because I'm a private individual who can ship all sorts of things. What "uniform shipping code" will keep me from suddenly deciding to send guns or gun parts into another country?

The truth is that Mexico is doing what it's always done. It's blaming the United States for the fact that violent criminals are getting guns while denying any responsibility in exporting actual violent criminals to the US.