You should tip dealers, especially when they're helpful. In the casino business, a "toke" is a tip. Dealers call tippers "George" or "live," and non-tippers "stiffs."
Dealers typically work for minimum wage (or close to it) plus tips. I compare them to restaurant servers because they provide a service and they rely on tips for their livelihood. The service that dealers provide includes properly handling your bets and winnings, answering questions about the game, being courteous and friendly, and just making your craps play more enjoyable.
Craps dealers typically share tips instead of keeping what they get. This makes your job of tipping a bit trickier. Ideally, you want to maximize tips for good dealers and minimize tips for bad ones (the same way you tip good restaurant servers more than bad ones). In terms of craps dealers, "good" versus "bad" isn't necessarily a measure of skill. Instead, if a dealer is friendly, respectful, attentive, and funny, I won't reproach him for being slow (he may be slow because, for example, he's new on the job). I'd much rather be in a slow game with fun dealers than a fast game with dealers who are mannequins when they aren't handling chips.
If craps dealers share tips, how do ensure yours goes to the good ones? You can't. If I'm disappointed in a dealer's service, I ensure his colleagues know I'm disappointed. When the bad one takes a break and a good one replaces him, I politely tell the good one something like, "I don't know if Fred is having a bad day or what, but he's been downright mean to the newbie on the hook." The dealer knows I've been tipping well and he usually gets the hint that Fred ought to lighten up if they want
me to continue tipping. Because dealers' income depends on player tips, the good one won't hesitate to insist that the lousy dealer get his act together. The good one knows, if I stop tipping, maybe others will, too.
If you're losing during a particular session, it's not the dealers' fault, so don't blame them. It's not easy to tip while losing, but you shouldn't base your tipping on your gambling success (or failure). When losing, if you can't keep the same tipping pace as when you're winning, simply slow down, but don't stop it altogether. Always remember that you give tips for good service, not for your success at the table.
For whatever reason, most craps players don't tip at all. I don't know if it's because of avarice, stinginess, or just plain ignorance. Usually, you're the only one tipping. Although not good for the dealers, that's great for you. It means you get all the dealers' attention and reap all the rewards. Rewards? Absolutely, positively, undeniably yes! Read my book, The Secret to Craps: The Right Way to Play, for details on how you can, indeed, benefit from tipping the dealers.