8 fuel injectors for a 6 cylinder car

Colletti Motorsports charged me for 8 fuel injectors when my car is a 6 cylinder.  My car, by the way, is a 1987 Buick Grand National.  Steve Colletti (the "ripper off-er") charged me $600 for a set of 8 - 50lb/hr injectors when he could have gotten better ones from any reputable Turbo Buick supplier cheaper. I am having 6 - 60lb/hr injectors installed for a total price of $425.00 at KDK Performance (more performance too), but Colletti Motorsports opted to make me spend more money for some reason, for less performance.  When I told him of this, he offered no apology or refund.  How inept do you have to be to do something like that?  Oh, I'm sure he was not inept.  I am sure he did it on purpose.  You see, many of these shady mechanics have only one supplier they work with.  That way they get incentives and "kickbacks" from their dedicated supplier.  I am most certain of this.

Here is my receipt with 8 fuel injectors charged to me.  At the time of this, I found the same injectors, but only 6 instead of 8, for $350.00 somewhere on the web.  I had written the number 350 down to remind me of how much I should have been charged.  The second pic is of recent injector prices from Jack Cotton's website.

There are also other hand written numbers on the receipt that I wrote.

Colletti Motorsports charged me $234.00 for the Number 2 and 3 Forged Main Caps.  I found them for $160.00.

Colletti Motorsports charged me $295.00 for Comp Cam and Lifter.  I found them for $219.00.

Quite a mark up for these parts, and I did not even go through the entire list.  Steve Colletti (the "ripper off-er") is nothing but a liar and a thief.