In my Line-X experience the only prep they do is mask everything off. No scuffing, no sanding, no nothing.
That **shouldn't** be the prep.
It has gotten far more lax than when I was in the liner business, but we spent 3-4 hrs of prep with a grinder & 4 1/2 80 grit hard disc. I would hit the 'valley' ribs hard, and the 'peaks' flat surface all to the point I was at bare metal you didn't want to rub without a calloussed hand, and even then your skin was left in the bed.
I was the guy( ~21-23) who operated the shop side, the owner ran the office side & did the phone & quoted all the drop-in customers - but for Rhino in early/mid 90's we were the shop you wanted doing your liner, even among local Rhino dealer shops. That owner has 3 shops now & I would prep my own & let his guy spray mine to this day. Good guy, ran a tight ship.
I know a local Line-X shop who went to the new franchise workshop, yet he only uses a D/A sander & scuff the paint. Regional Line-X shops know he's a slacker & won't repair his sprays. My stereo shop buddy used them when he was just opening & his personal liner pulled up a 1ft sq area, without him picking at it. Sad.
Their response was "you peel & re-prep, we'll shoot it" - he knew my days in Seattle & he asked me - I was amazed at how low the average guy is treated, especially since they came onsite to my acid refinery & did a flow catch-bin area we let acid flow like a sewer, treat to neutral Ph & let drain days later.
It's 100% the prep to how your liner lasts & performs - when my Tundra goes to the Rhino shop I'll do my prep & let them mask & shoot.
A D/A sander with loose grit (<200 for sure) -is fine on the sides of a truck bed, but you need ~2hrs w/ a coarse disc on the bed floor to really get tooth worth calling a 'lifetime coating'.
My way let a guy keep his bar oil dripping, gas evaporating, no guard on the bar, --chainsaw in the bed flopping sometimes & all it did was make little cuts in the liner & make the liner soft when gas hadn't flashed off yet.
In my 2.5yrs doing this while in school in Seattle (Everett shop location) - I did maybe 1/2 dzn patches, and most were forklift damage - 1 was chainsaw & logger damage where my GF who lived in Forks (yeah, the Twilight Forks


) -was why I logged & guys brought their work trucks to me when I was back over here on weekdays since I claimed 'you break it, I respray it'.
I think it was 3 in that time that were my Forks buddies, and only 1 was the chainsaw thing.
Back then there was only the single Rhino formulation & a bed was $900, but our prep meant guys brought a truck from all over the Puget Sound to our shop. And why the newly minted owner then has 3 locations now. His ex-wife has 2 locations she got in a divorce, so you could say he'd grown 5 locations.
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:::Cliff Notes::: ---Prep is everything, if functional liner then going bare metal & rough tooth isn't overkill. Like paint, prep is everything to final result.
You're buying the prep, and also ask the repair policy from the franchise owner prior to paying. It's a PITA to pull liner for repair w/o the right tools.
HTH everyone.