I've never used a carbuying service through BJ's or Costco--but I did use the one through my credit union, and it was fantastic. I can't recommend it enough! I went online, and picked out the car that I wanted and they gave me a dealership to go to, about 1/2 hour from my house...I went directly to a specific salesperson, gave him a certificate I had printed out from my credit union's car buying service website, and we test drove the car. When I told him I wanted it, he took me back inside to a computer, and he showed me the price, it was almost $5000 off MSRP, not $5000 off the sticker, but MSRP (which is much lower than the sticker). There was no bargaining, or anything, that was the price, and you could use the dealers financing, which was not a good deal at all at the time, or bring your own financing to the table, which I did from my credit union. I traded my old car in, and left without putting any money down at all, returned the next day with a check from my credit union for the cost of the car, and that was it. It was the easiest car buying experience I've ever had, and I got the best deal (I looked for 2 months before going in there). I'm sure that the BJ's/Costco buyers are similar--but the ease of the entire thing was what sold me too!!