Unless it's specifically formulated for acid loving plants, I wouldn't advise using a bagged potting soil. This is an issue that's been discussed before, so, if you haven't already, try to do some targeted searching in this forum.

Highlander, I'm not an expert but I just prepared some new beds for 8 blues arriving tomorrow FedEx. It has been repeated on this forum the benefit of Sphagnum Peat Moss and Pine Mulch mixed with or without native soil. Link below for some reading and I am hoping a source that will be providing me some nice plants.

Do a forum search as well. There are many experienced berry growers here that have already typed volumes.

Chad

Here is a link that might be useful: Planting Guide

HighlanderNorth, I grow in pots. So, I have no direct experience in preparing soil. However, the publications I have read indicate that adapting the pH of soil to successfully grow blueberries takes a number of months. Here are a few links you may find useful:
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19660/ec1560-e.pdf
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/12202/ec1304.pdf?sequence=1
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19772/ec1585-e.pdf
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/20444/em8918.pdf

There are a bunch more out there. Both Cornell:
http://www.fruit.cornell.edu/berry/production/blueberryproduction.htm
and Michigan State:
http://blueberries.msu.edu/
have sites with lots of blueberry information.

Good luck with the blueberry bushes!

If you plant the blueberries in clay they will die. If planted in clay the owners will have to do alot of up keep to maintain the ph and water requirements. Speaking of water, if they are watering with municiple tap or hard well water the plants will die aswell. Not trying to sound negative, just being honest. Blues are very easy to grow IF you have the right soil, water and knowledge to grow them. I would suggest doing alittle home work on what they require before planting them in the ground. I also have to deal with clay at my house. Instead of planting in the ground I make raised beds 12inches high of 2/3 pine bark mulch, 1/3 peat moss and 1/3 sand and then top them off with 3 to 4 inches of pine bark mulch. Good quality water is a must. I have about 1400 gallons storage for rain water and that probably still isnt enough to get through our hot summers in Houston. Again, not being negative here just giving you the facts. If you are running a business your customers wont be to happy when all there bushes die in the first 2 years. May be you can talk them into pots for the blueberries and plant something else edible in the bed. Pots or raised beds are much more productive for blues if the local soil is clay. Good luck!!!

To Blueboy1977: I mentioned in the OP that I will NOT be growing these in clay. I will be removing ALL clay and getting rid of it, like I always do regardless of whatever I plant for the most part.

As far as the search function, I have always had nothing but heartache when using forum searches. I will type in a basic search parameter, then press search, and I almost always get completely unrelated threads about completely unrelated topics. Its never like a Google search, where the results are EXACTLY what you asked for. Instead, you get stuff that might mention one or two of the words in your search, but its usually not even about what you're searching for. So I end up wasting time not finding the info I needed.

So when someone tells me "just do a search", I always wonder if it's sarcasm, and I wonder where is the LOL or LMAO at the end!

Highlander, I understand you will be digging holes to place the plants but the surrounding clay will still raise the ph of what ever media you put in the holes. Do you know what the ph of the native soil is where you will be planting them? Clay is very hard to amend and keep the ph where it needs to be plus drainage my be a issue during prolonged rainy periods. Blues require good drainage or root rot will come into play at sometime. As far as bagged soil goes if its not made for acid loving plants I wouldnt suggest using it. There are bagged soils for Azalas that will work. Ive read about alot of different blueberry soil mixes and Ive used several mixes myself. All have done well for me so far but they have consisted of pine bark mulch, peat moss, sand and perilite for potted plants. Ive gotten partial to mostly pine bark mulch mixes with some peat and sand for raised beds. This mix works also for pots but if I have perilite I will use that instead of sand but both methods will work.

Highlander, I feel your pain when it comes to using forum search engines, even here at Gardenweb. They're really quite lousy. One strategy I use here: use Google, but include Gardenweb in your keywords. Example: Gardenweb blueberries soil. It's not perfect, but it helps.

Marc- you can improve the Google search a bit by limiting the results to Gardenweb itself. For example:

site:gardenweb.com blueberries clay