First and foremost, take your time transferring and don't move large amounts in a rapid fire manner. It honestly depends on how much you intend to move, but if you go the shop method, I would advise against making a junk item cost something like 99k or 350k because that'll be suspicious to TNT. Try to do it in smaller increments, like maybe 50k or so.
If you'd like to do so via the trading post, again, take it slow. Don't just offer 1 or 2 mil on junk item because you'll again be flagged. Do smaller amounts like around 100k.
Also, space the transferring out. I'd advise doing this all in one day. Try to maybe span it a week or so, but again, it depends on how much you're moving.
Lastly, I personally would avoid moving via the auction house due to how public it is. I also don't recommend using the shell to buy higher end items that you can then just move to your main to resell. Most people are suspect to selling to shells and they could end up reporting you.
Regardless, good luck moving!