Some people have had bad experiences/expectations. Some people simply can't seem to read the disclaimer on every page regarding ship times. Some people say PSA sucks simply because they read someone else had a bad experience.
I, however, have had nothing but good experiences.
My first psa order was for 4 Anderson lowers for $49 each with free shipping. On the site it said they would ship in 15 days or sooner. They arrived 20 days later.
The next order was for 2 lower build kits, one complete, one not, and a complete barreled upper. It got to me in about 25 days.
I built two lowers, one had a sloppy safe/fire selector. I swapped parts and determined it was the selector itself and poor machining. I called psa ( be aware, if you call customer service, you will be on hold for at least a half an hour, put your phone on speaker, and do something else while you wait). I talked with Everett, and they sent me another selector the next day at no charge. They Did not want the old one back.
My third order was for another barreled upper, carry handle, and range bag. Shipped to my door in 20 days.
I just ordered 4 more stripped lowers for $49 with free shipping. They shipped in 10 days.
I think PSA is fantastic, they have great deals, their customer service is fine, and they ship when they say they do.
Just understand that you are trading same day shipping for low prices. Put your order in and forget about it. It will show up when it does. If you are someone who wants instant gratification of buying something, get it elsewhere.
I have heard initially there were QC issues with the PTAC stuff ( their lower line). I'd stick with the freedom or premium line.
Unless you want the fun of building an upper yourself, you can pick up a barreled built upper for less than you can buy the parts for if you catch them on sale.
Sign up for their emails and you'll get daily deals in your inbox.
They also have an industry forum over at ar15.com where they answer questions, address order concerns, etc.
Just my 2c, but as far as I am concerned they are good to go and I will continue to buy from them.