My sister arrives in a week's time and has pre-booked and paid for the overnight sleeper from Hualamphong to Khon Kaen.

Does anybody have any idea where  the ticket collection point is?   Thanks very much.

If it was done on the SRT e ticket website they are sent by email. See: https://www.thairailwayticket.com/eTSRT/Default.aspx?language=1

How did you book and pay for them?

Thanks for your prompt reply, Joe.  I didn't book them, she did.  I'll ask her.

The answer is that she booked the tickets via 12GO and they told her their office is across the street from Hualamphong station.  Can anybody be a little more precise please?

I had never heard of them, but did a Google search.

Website:  12go.asia/en/offices

Address & detailed directions are given there.

Allan is on it, no problem, close to the station 

Unfortunately another victim that has been ripped off by those criminals from 12go.

The booking fees almost exceed the value of the tickets.

I used them once in a desperate situation during Songkran because they buy (illegally) tickets for whole carriages and re-sell them.

Never ever again.

SRT online ticketing system works smooth now, no need for those agents anymore.

Or does anyone still buy flight tickets at a travel agency....?

How do they "buy illegally" train tickets without the connivance of the SRT, especially a whole carriage ?

Several years ago, I lived relatively close to Hualumphong for seven years, and for that reason, was a relatively frequent train user for out of town travel.  Almost anytime I went there, I was approached by vendors on the sidewalk, purporting to sell train tickets. And this, with no knowledge of where I was going, or even if I was planning to travel. (I used to buy my tickets in advance, so was there without luggage, at that point.)

How could these people, whoever they were, supposedly sell tickets for less than the SRT ? The fact that this was always happening must have said a lot about the gullibility of travelling farang. These vendors never approached Thai people. I always presumed that they must have been selling worthless pieces of paper.

Not quite that-they were then told (remember the Grand palace gag?) that so solly, tlain now full-special holiday Thai for Budda, but we have BUS for you.