Basically, if they are wet, sticky, tacky.

Many printing techniques (but not all) fuse liquid resin into the desired shapes. When finished, the object is drawn out of the liquid resin tank it was printed in "still dripping." It then is placed in a UV curing "booth." However, for various reasons, it may not be left there long enough. If you receive it, and it is still covered in liquid resin (wet, sticky) or "sticky/tacky" feeling, you got a part that did not spend enough time in the UV booth. You need to finish the job by putting it in sunlight for a bit. Monitor it, and don't overdue it. You might need to "flip it" to ensure even curing. When it is no longer tacky, it is done.