What are the risk of buying and selling at market price?

Are there any negative points or risks involved with regards to buying any scrip whether liquid or illiquid at the market price? What is stopping the order to hit the upper or lower circuit limit or just hit 0 when we order at current market price?

Buying at market price ensures a complete fill of your order but does not necessarily guarantee the price and you will end up paying a little more per stock even in liquid stocks depending upon your volume(but it also has to do with the liquidity at the given price point, more often than not you will get a good price) but as it ensures a complete fill, it could be worthwhile to use it when trading in large volumes and in liquid stocks. In illiquid stocks the risks are significantly higher because there aren’t many sellers in action in the first place so once you fire your order the price may vary by a large margin before your order is filled.