I once had my visa application (tourist) delivered by a friend, but I picked it up myself.

Would it be possible for a friend, to bring and pick up ones passport - or will you have to appear in person?

They same question goes for: border crossings and visa extensions (like the 30 day you can get from immigration in BKK)

Is it possible to get a friend, or a company, to do it for you?

As far as border crossings are concerned this is very obviously illegal, both according to Thai law and the law of the country which issued the passport. Most passports contain a text saying the passport should only be surrendered to competent authorities, and this clearly doesn't include Mr. Jimmy's visa service. Your passport is supposed only to travel with you, especially when the travelling includes crossing borders.

A visa service is legal and accepted within the same country. Travel services obtain most visas in developed countries. But stamps indicating border crossing without the holder would be totally illegal and considered suspect terrorist activity in todays world. As for visa issue it would be up to the Consulate involved.

That said; the only sure way you know the stamp is real is if you do it yourself. There have been false stamps used in this region.

There was a crack down on these passport runs with out owner a few years ago, many travel agencies raided and passports confiscated