Had a new string put on my bow. Took some shots when I picked it up. I also installed a new sight. Was hitting right, so i adjusted sight right..well I had to move to sight almost so far right I almost ran out of room to hit bullseye at 20yards. When I brought this up to him he said it's cause the way my eyes are and too big of a peep..I could understand. The peep thing but then I would just be less consistent. So he said the bow is perfectly tuned, rest centered with string and nothing he can do...anyone think that's BS?

What bow? Sounds like Cam Lean could be one issue, not all bows are center of rest when properly aligned. Just string or string and cable or cables replaced? Is the D-loop ties with the knots going opposite directions or the same? The D-loop knots should be opposite or you will be torquing the string every time.

Just a few things that are easy to miss on a string and cable change out that can throw things off. Timing of the bow also comes into play, not as simple as just take the old ones off and put the new ones on

Shoot it through paper. "If" it's properly tuned you'll know quick. If not find a better bow tech.

What bow shop so I know not to use them. Thats BS.

Try a modified french tune.
1. Hang a string vertically on a target like a plumb bob. Shoot at the string from 1 yard. Adjust only the sight left/right until you split the string, or at least touch it.
2. Then shoot at 20 yards or further. Adjust only your rest left/right until you're on target.

You can repeat the process over and over again making smaller adjustments each time until there are no adjustments to be made. Typically once is enough. This well set your center shot without messing with cams or strings. Make sure you broadhead tune before you go hunting.

You can paper tune/walk back tune/French tune all day and if timing and or cam lean... are off the bow will not shot as well as it can until resolved. Those are all good things to do but are not resolving the issue unless everything is set right on the bow. Very few if any string and cable sets have the right twist for timing and yoke tuning when put on no matter who the manufacture of the strings is.

New string and cables. It is a Diamond Marquis, single cam set-up. Also left-handed, 10 years old but still in great shape cause I never had time for about 5 years when I was in the service to shoot/hunt.When I dropped it off I mentioned checking cam lean and timing. He held it up, eye balled it , and said "nah its good, everything is lined up." I didn't like that but a friend referred the bow shop and said they were good, so I figured I'd try them cause there aren't too many options down here in the RGV. 2 years ago a guy at basspro-Harlingen dry fired the damn thing. The D-loops are in opposite direction. The bow was doing the same thing last year so I wouldn't shoot past 25 yards cause I had to compensate for drop and horizontal drift. I mentioned this to him cause I know something is off mechanically and he said, "oh yea, its your eyes and that big peep." I knew he was full of sh#t but didn't even want to have him try to fix it at this point. Did not even offer a paper tune, walk-back, nothing. The funny thing is they have a pretty good reputation around here. I guess cause the only other option is Basspro.

I am too far to look at it for you. Perhaps if you leave the valley sometime find a bow shop along the way and take it with you. With a dry fire in its past I would ant it throughly gone over.

Finally got a chance to work on it. Adjusted rest left and moved sight back to the left. Hit right on at 20yards, went up to 10 yards and right on. Then back to 35 and also right on - horizontally and about 7" low which I would expect. I'll double check at some further ranges but it seems good to go. However my D loop keep getting in a little tangle after just about every shot. Any ideas why this is?

Twist in the material when tied.

Ok that's what I was thinking. I really need to just start doing my own bow work. I cant believe that tech didn't even think of moving rest windage.