They are asking absolutely within legal terms. SGI is a old reputable name approved under SECP and JAMA PUNJI. May be u didnt hear because mostly they operate with corporate.
1 security check is for them to pursue legal action if ur 2 consecutive checks bounce. Even if i give something via checks, it makes total sense. They are bound to return this check once, car clears. it's an excellent deal, new is new., best thing is ur maximum amount is with you... earn on that too... invest somewhere else and enjoy car on installment....