I'd assume the initial question was regarding certain listings on Market that have TC + ST prices.
That's a feature available to Premium shop owners: they can sell you items even if you don't have a high enough belt for it - in that case you pay an additional fee in Shiai Tokens depending on your Qi. That fee, however, is paid to the system so the seller doesn't receive it - so essentially you can buy items for TC + ST, but you cannot sell them for ST.