I posted in this thread last night. part of the post was links showing the difference in the mouths of Pekoltias, Panaques and then added an Ancistrus to show what an algae loving fish mouth looked like. I was unable to complete the post as PC went down before I grabbed the 3rd picture URL, so I did not make the post. But the mouths make telling the difference between similar looking Pekoltias and Panaques easier. This is way more reliable than coloration or patterning which can be variable and similar, especially when the fish are stressed.
In that post I commented that the site selling the fish is notoriously bad on its pleco labeling. When they first expanded into the live fish business I emailed them several times about this problem for several different plecos. They did not respond, they did not correct their mistakes and, clearly, they continue making them.