-- Last Updated: Sep-28-12 2:56 PM EST --
When I bought my P&H Delphin 155 it came with decent size dents from being displayed on rigid stands in the showroom. These were very obvius and not minor at all, but I thought they were not permanent and I did not think the plastic was deformed beyond repair. I had corrected very similar dents on the same kind of boat in the past so I hoped to do the same with this boat or return it if unsuccessful. Because the boat was not full price (way far from it, actually) and the dents were not terrible and all else was good, I was willing to accept the condition.
I was able to eliminate them with heat - careful application of my heat gun and leave it to cool off with some yoga matts in the cockpit to keep the shape while it cooled off. The dents are no longer there.
I would be annoyed if they remained, however. I've seen a brand new Tempest 170 on display with such severe dents that I would never buy that kayak even at a very low price - the plastic on these would be so stretched as to be a permanent deformation. Large dents weaken the already weak rigidity of a long plastic kayak like the Tempest and you might actually feel the effect if you go out in rough water. I don't think it will have much effect on speed unless you paddle full speed all the time (in which case it would matter some).
So, decide for yourself how much it bothers you. And if the dents seem minor, see if some heat can bring them back to shape, then store it properly so that they don't come back. Just be careful with heat - you can do new damage if you overdo it...