One old guys opinion...which like necks..everyone has one.
Then one thing in life you dont want to haggle over price is a well done tattoo. You get what you pay for and wear it for years.
Do your homework. Plan well in advance and research your artist, style of work you are seeking, and what you can afford to pay.
My artist gives very realistic estimates. Small pieces are an exact price. Large pieces are by the hour. When working on a piece that requires multiple sessions, you might find some days you may sit still longer than others. Factor in touch ups a couple months once the piece is done. Detailed color work in seldom done once and finished. Everyone's skin type, healing and other factors suggest additional work will be required. A good artist will be far more critical than you are. He/she will go to extreme lengths to provide work that represents their skill set. Happy customers come back and tell their friends in today's world of social media.
Set up time, allowing your artist a smoke break, allowing you to stretch, bs conversation are not included in an hourly fee. My artist is very realistic about backing out time paid from the minute I walked in the door to when the machine started buzzing. In return I tip well, bring gifts and send business.
Question would you go to your favorite restaurant and haggle over the menu price? If you think tipping for good service is cool for your attractive waitress/waiter for a service that is one and done. By extension you are going to wear this ink for years....treat the artist with the respect the intended task deserves.