when you want to buy items with qi,do you need to have the cetain amount of qi when you are buying it from someone?

Yes.
Th people who can transfer items without QI restrictions are members of the msquad.

when they are members of the market squad, do the item prices go alot higher?

The general prices does not, but if they sell something to someone, that the user does not have the qi for, then it costs a lot more.

Example: Ninjabent asks the Msquad how much I can buy full Elf for. They see that I don't have 15000 Qi (which is what I need for elf), and then they tell me that I can buy it without needing qi, but it will cost a lot more.

maybe i think

Thats kinda wrong. Members of the M-Squad cant transfer them, but we can get a TSA(Torishop Admin) to do it.

Yes the prices are much higher for no qi items. That is because you dont have the qi for it, so we raise the price to be fair and to keep the items somewhat rare.

Answer me this why is pure force 1.5k but kids sell it for a lot more.

Thats off topic but pure force cannot be bought from the shop anymore for tc. You can only use USD to buy it from the torishop, so people can set higher prices for it.

why now use dollar's?

Because Nabi(the company incharge of toribash) is a business and businesses like to make money. Thats basically the whole reason.