I have ordered from PP as well, however I didn't have any problems that required interaction with their Customer Service department. I would say everything went smoothly with them.
Unfortunately I didn't have as much luck with Carpartonsale. Carpartsonsale did something similar as Carparts.com when they sent me three front shocks and one rear shock. Unfortunately, they are just a middleman and I have my doubts as to whether or not they keep anything in stock. The day I received my shocks, I called them up to tell them they sent me three shocks. No problem, they sent a USP call tag for my extra front shock to be picked up and they would send me another rear shock ASAP. They didn't have any in stock so they had to call around to all of their sources around the US to find someone that had it in stock. They finally located one and had it sent UPS Red about 10 days after I sent my extra front shock back.
Right now I am currently waiting to receive another rear shock from them. One of my rear shocks developed a leak, so I called Edelbrock. Edelbrock told me to contact the place that I bought them from to arrange for an exchange. I contacted Carpartsonsale and the only thing they offered was for me to send them the faulty shock; when they received it they would send me out a replacement or I could buy another one from them and when they received my faulty shock back they would credit me for the shock I just bought. Since the leak seems to be somewhat minor I didn't want to risk them telling me there is nothing wrong with it, sticking me with an extra rear shock, I elected to just send them my faulty shock. My faulty shock was signed for by Carpartsonsale on 5/11 however my e-mails to them go unanswered as to when I can expect my replacement shock. I am getting tired of the rearend wallowing around on every bump with only one rear shock. I think if they cared about customer service they should have offered to ship me a shock for immediate replacment and if I didn't return the faulty one within 14 days, then charge my card. Oh well, I'll consider other suppliers the next time I make an on-line automotive purchase.