The only thing to do would be to try pressing some - there 'should' be a temperature where the polyester starts to soften and it can be pressed into a fold, but it all depends on what the polyester is and how it has been treated - the required temperature might be too high, the cloth might spoil, your iron might not have an accurate enough control on it for the job - too many variables.

If it is a really good looking fabric then I'd say get it anyway, press it gently and then sew the edges of the pleats to make sure.

The edge stitching can be an attactive feature of the pleating, if done to show, or just about invisible if you want it hidden.