Tips (gratuities, bahşiş in Turkish) are generally modest in Turkey (a small percent of the price paid). Because Americans tend to tip big, leading Turkish tourism industry workers have been led to expect big tips from Americans who travel to Turkey.
In most cases, you cannot include the tip on a credit card charge. You should tip in cash and, in most cases, hand the tip directly to the person who has served you. (In some establishments, any tip you leave on the table will end up in the owner's cash register, not in the server's pocket.)
Although the person you tip would probably prefer Turkish liras, you may tip in any currency so long as you give notes/bills (paper money). Don't give non-Turkish coins as these cannot easily be exchanged for Turkish liras.
Every airport, bus station (otogar), and train station (gar) has an official tariff for porters, which should be posted prominently. Of course you probably won't see it, so tip about $1-$2 per bag, which should be plenty. If you actually end up underpaying according to the official tariff, the porter is sure to let you know!
For taxi drivers, don't tip, just round the fare upwards to a convenient amount. For example, if the fare is TL107, round it up to TL110.
For private transfer services, no tip is required, though if you wish to tip—if the driver has been particularly obliging—5% to 10% of the fare is appropriate.
Tipping at restaurants has become much more common and expected throughout Turkey. A tip of 10% - 15% is considered appropriate at most places. You can leave it in cash on the table, or ask the waiter to add it to the bill.
Porters are happy with $1 to $2 per bag. Housekeeping staff are hard-working and deserving of your generosity. In moderately-priced hotels, $1 to $2 per day is well-deserved and greatly appreciated.
In some hotel breakfast rooms, restaurants, and/or at the reception desk you may see a Tip Box. This is the appropriate place to express your appreciation to waitstaff for good service.
Tips to guides and drivers on organized tours are at your discretion. Certainly guides and drivers hope for tips, but a good guide or driver will not think less of you for not tipping; and a bad guide or driver deserves no tip.
Remember, this is a tip meant to signify good service (if that's what you've received), not his/her payment (which you will already have paid by paying for your tour).
That having been said, US $20 to $40 per day from a small group would be appreciated by the guide, somewhat less for the driver.
This is the total tip for the entire group, not the tip per group member. So for a 10-day tour, the guide would be given $200 to $400 total from the group as a recognition of his/her excellent service.
If a site guardian performs some special service, such as giving you a personal tour, a tip equivalent to a few dollars is appreciated.
When you visit a Turkish bath, or Hamam, at the end of your bath all the attendants (and there are lots of them) will line up to "bid you goodbye" and expect a tip (if service has been good). Share out among them about 15% of the total price of the services you've used.
—by Tom Brosnahan