Having done fostering and adoptions, I would add these comments:
1. Most rescue groups will NOT "hold" a dog for a possible person. They are trying to get the dogs adopted to good homes as quickly as possible. Telling Suzie who is standing in front of me "No, we have someone coming to see the dog in 2 days, so I can't let you have it now" is losing a definite home for a maybe home. Many people will swear on their lives that they WILL come in 2 days - only to never show up. Get over this expectation - it's NOT going to happen.
2. Some rescue people are nuts; some have no sense, common or otherwise; some care more about getting the dog out of their home, than they care about getting the dog a good home. If you think the person you're dealing with is one of those, ask for a different volunteer to help you. (See next item)
3. Rescue groups are made up of volunteers. Most have full-time jobs, families, etc. in addition to their time volunteering for the group. Most rescue groups are desperate for volunteers and continuously operate on a volunteer shortage basis. Some of the volunteers are less than spectacular - but when you aren't paying, you aren't getting the cream of the crop. This all means that messages will get lost, return calls may get forgotten, miscommunications will occur. Be patient and polite but pro-active, and you'll likely get a good result. Act like a nasty SOB and they'll drop you real fast (no-one wants to adopt a dog out to an SOB).
4. If the rescue doesn't think a particular dog is right for you, LET IT GO. You're not going to change their minds by arguing over it. Whether they are right or not, it's their decision. I have turned down people for a particular dog, had them argue with me for an hour or more - only to find out that I wasn't being mean: the dog was not a good fit for their family and nothing was going to change that. Likewise, if they suggest another dog, don't just blow it off. Give that dog a chance - you'd be surprised how many times the dog you thought you didn't want is actually the perfect dog for you (I currently have 2 of those perfect dogs - because I gave the foster mom a chance at being right).