The entire process is to make sure the wine is not bad, it's not to let you decide if you like it or not.

They should present you the bottle, you would check to make sure it's what you ordered, say for example they did not grab a different year then what you wanted.

They should then remove the cork, and if it's a red wine give that to you for inspection. You look to see if the cork is labeled with the wineries name (if you know it should be) if it's not then you probably have a refilled bottle. Some people smell the cork to see if it's bad, others look for the amount of sediment on the cork, and if the cork is dry, that means the wine was not stored on it's side, and it may not be what you were thinking it was.

They will then pour you a bit of wine. You want to smell to make sure it has not become vinegar, you won't want any musty cork odor, and unless it's a very old wine, it should not be cloudy but clear.

You then take a sip and make sure it doesn't have that musty corked taste, and then let them know it's a keeper.

But the only reason to refuse it would be if the wine is bad, if you don't like it, but it's not defective, you are pretty much stuck with it.

If the restaurant serves the same wine by the glass, there's a good chance they will let you sample it first before you end up with an entire bottle you are not happy with.