KamilKoc has a great reputation and founded 1926 it is one of Turkey's venerable bus travel companies. In my experience, however, there are severe dents in KamilKoc's reputation.
When moving to Fethiye, Turkey I arrived with lots of luggage at Istanbul's Bayrampasa bus station. There I bought a ticket for 95 TL from KamilKoc's ticketing office. This was already quite a procedure because all customer service agents appeared to speak English worse than I spoke Turkish. Nonetheless, we got it settle and I ended up waiting in an overcrowded and noisy waiting hall. Interestingly, I made the acquaintance of a police man who was under cover hunting criminals in the ticketing office. Hmm, why would KamilKoc has so many problems with criminals?
The big Mehhh came when I bored the bus with my luggage (1 suitcase and 8 bags.) The bus bus attendant wanted 30 TL extra. Why extra for luggage? The Nisikli bus travel company (http://nisikli.com.tr/) didn't charge me anything extra. Also, I showed the ticketing cleark my luggage and he was ok with it. So why did I have to pay to the bus attendant now? My feeling of being fleeced grow stronger when I offered to pay the 30 TL by credit card. Having just arrived in Turkey I had no cash yet. But the bus attendant insisted I had to pay cash or I cannot travel. Having no choice I had to go and find an ATM at the bus depot - that was risky because these where all ATMs from unknown companies. If my card was retained I could end up stuck in Turkey without any cash what so ever. Fortunately, the ATM withdrawal worked the bus attendant got this 30 TL which he put straight in his own valet. Yes, I was being fleeced and KamilKoc ticketing clerks did not care.
Having read the article about an overnight bus travel on http://www.turkeysforlife.com/2012/06/fethiye-istanbul-turkish-intercity-bus.html
I expected more food and comfort during the trip. I only got one small glass of water and later a tea and a cookie for dinner. Fortunately, the bus stopped often so I could enjoy the delightful Turkish cuisine and not starve before trying to get some sleep at the not so comfortable chairs. (Mercedeces busses have better chairs).
In summary, riding with KamilKoc is a decent way of traveling but because of the bad service and problems with my luggage it no longer deserves a high reputation.