An off-center or unexpectedly positioned print is one of the more common complaints in print-on-demand, and it's almost always a placement template issue rather than a print quality issue — meaning it's avoidable with a proper understanding of how these templates actually work, rather than something that just happens randomly.
Most POD platforms provide a placement template or guide showing the exact printable area for a given product, often with a default position (usually centered horizontally, positioned a specific distance from the collar) already set. The mistake a lot of sellers make is uploading a design and trusting the default preview without understanding that the actual print area boundaries and the preview you see on screen aren't always perfectly WYSIWYG (what you see is what you get) across every platform and product type.
A specific, common issue: designs that look correctly centered in the platform's mockup preview can print slightly differently positioned once actually produced, particularly for products where the exact print area varies slightly between different sizes of the same garment (an XL shirt has a physically larger chest area than a small, and some platforms auto-scale placement per size, others keep it fixed, which produces different relative positioning across the size range).
The safest habit, beyond trusting the on-screen preview: check whether your specific platform lets you preview placement across multiple sizes, not just the default one shown, and adjust if the positioning looks meaningfully different across your size range. If a platform doesn't offer this preview, ordering a sample in both a smaller and larger size before fully launching a new design catches this kind of size-dependent placement drift before a customer does.
Text-based designs are particularly vulnerable to placement issues, since even a small vertical shift can move text uncomfortably close to a collar or shift a design's visual balance in a way that's more noticeable than it would be for a purely illustrative design. If your design leans heavily on precise text placement, it's worth extra scrutiny at the mockup stage and, ideally, a physical sample check before committing to a full product launch.