First of all, I heard, from hanz0, I believe, that TC sellers shouldn't lower the price of TC too much in order to keep Nabi's profit high. The defined limit was the one that Hector used in his shop, which was about 10$ for 100k.
I've seen multiple threads, like this one or this, which offer larger amounts of TC for lower payments. If I wanted to sell more TC, I could just make multiple sales to bypass the limit, instead of creating a shop.

Second, as I've seen in some TC shops, like Hector's or Ash's, they offer, for example, 500k TC + 100k TC for 50$. As far as I know, 500k + 100k = 600k, which would cost 60$.
This just looks like another way to bypass the previously mentioned limit.

My questions are:
Does the TC limit still apply to the current TC shops and does it even apply to TC sales? And what about the bonus TC additions, are they legal?

PS: Posted this thread here as it might have some discussion potential.