The quality of customer service in Istanbul is fundamentally special, wherever you go. No 'exclusive' customer of retailers like Beymer, Burberry or Prada, in Nisantasi would expect anything less. Tea, coffee, wine and newspapers are all part of client hospitality. Laws are breakable = smoking is allowed, and customers can bring pets and food into the shop. Shipping, loyalty cards and financial services are all part of the package. Beymer will collect customers from their hotel, Burberry will take clothing to customers' homes.
But go to your Bakkal [mini-market], butcher or baker, in any Istanbul neighbourhood, and the standards are relatively the same. A chair, chai or water would be offered, time allowing. Cigarettes are offered liberally and pets are welcomed. Credit books are common currency.
Local shops will give out magnets so customers can phone through, or shout down an order ('Bakkal, Bakkal' is a regular call from apartment windows), and the shop staff will pick and pack your groceries and deliver them to your doorstep at no extra charge. If they don't have a something in stock, they'll run elsewhere and get it for you in 15 minutes.
If you trust the shop and the shop trusts you, they'll agree to look after your house or car keys while you're out. The local shops use the same customer service as global businesses, to keep themselves alive. One likely difference is that the local shops are controlled by parents, not by parent companies.