No, ya can't start blaming the end-user for your short-comings. There are certain questions the sign guy/gal must ask before starting a project, such as this. You need to know what kinda paint was used and how it was prepped and how long its cured. Is the place in a climate controlled area. Is there insulation behind the wall. Knowing what direction the wall helps in some cases.
We've put up literally 1,000s or probably tens of 1,000s of signs, both vinyl and rigid substrate on interior walls with practically no failures over the last 15 years. We've had maybe 2 or 3 failures and it was always the paint did not have enough time to cure. However, one wall started to weep. It actually would sweat come around 1 or 2 in the afternoon, then it would stop at night. Turns out, when they remodeled the building, they added this and added that and never told us, when they put the extension on this one wall, nothing was between the outside wall and the sheetrock. That air buffer acted as an oven and the heat built up since this was a southern exposure. With the interior being climate controlled, it would sweat and our stuff did not hold very well. The builder got in a lotta trouble for cutting those corners. He sidetracked the original plans, but didn't tell anyone. Ended up costing him a mint to make good. Afterwards, we went back and re-hung everything and never another problem in that particular building.