As a girl with experience both with RueLaLa and Proenza (especially damaged Proenza), I think I can add something to the conversation!
In December, I bought a PS1 Medium in the black/white geometric triangle pattern at
Nordstrom. It was on super-sale and was a complete impulse buy. I had been pining over the PS1s for years and this was the best price I had seen! However, I must have used it for about a month and I noticed that the clasp was falling apart. The little bar that holds everything together was falling out, and it was impossible to close the bag. I had heard that PS was great with repairs and sometimes even gave a free wallet for the trouble, so I decided to go to the Madison Avenue store in NYC while I was there on vacation and ask for advice. The lady was very nice until I mentioned that I bought the bag at
Nordstrom. Her whole attitude changed (I still cannot figure out why, since as far as I know Nordstrom is a verified seller...) and she said I needed to go through my Nordstom store. I did, but Nordstrom sent my beloved bag to a third-party bag refurbisher (who the saleslady informed me was very trustworthy and that they sent all their bags to him). The bag came back fixed, but I was disappointed that PS couldn't help me out. I was nervous sending the bag away.
RueLaLa is a great site. You can't not love it. But with my past experience with PS and a broken bag, I would definitely be wary of buying a bag from RueLaLa if it is a PS1 or the likes. From what I have heard, I am not the only one who has had issues with the PS1s lately. However, I did notice that RueLaLa has had some super cheap wallets and cosmetics cases up, so for those I think it's fine--they don't have many components that could be defective.
In all it's up to you. You can definitely find someone to fix your bag if something does go wrong, but in my opinion it shouldn't be that difficult! It really depends if you can justify the discount to the risk. But I would definitely keep an eye on the forums on account of the PS quality issues!