Hi all,
I just wanna know how merchants deal with the changes in bitcoin value.
Do they update there prices in bitcoin all the time and cash out immediately?
Sometimes. There are a few different sites where you can do something like post a $20 price-tag on an item where BTC is accepted. For example:
http://fizzisist.com/priceimg/img/20 (change to what you like)
Various exchanges and other-suchs offer payment processing and merchant solutions where it's done similarly. Generally, everyone uses Gox prices. Some update every 24h, 1h, or quicker. Listing sites like BitMit also integrated the ability to price in USD, where the BTC price changes based on exchange rate.
BitPay, however, will give BTC price based on USD and automatically cash out at the time BTC's received - if that's what you want. They will also direct-deposit right into business account for a fee.