Lots of great advice, so I'll add an anecdote to underscore the need for the buyer to be present at the survey.
When we purchased our first Sabre, I was not present. Fortunately, the boat was only 4 yrs old, there were no significant problems, and we kept her for 16 years. For our current boat, I made sure that I was on board before both the broker & surveyor (I'm a bit older & wiser now) on survey day. Gail Browning went through the boat while in the water (interior, rigging, engine, etc). We then moved the boat to a hoist area and discovered a very tight shifter cable. After boat was short hauled and put back in the water, the broker called a mechanic to fix the shifter (at the owner's expense!) while Gail continued with the interior sounding the hull, bulkheads etc. At one point, I heard "Uh Ooh...this isn't good...". She'd discovered a delaminated bulkhead in the head to which the port lower chainplate was attached. The chainplates hadn't been caulked and water leaked below and rotted the entire bulkhead. Prior to making an offer, I'd sounded the bulkheads, but had missed this one, so she'd earned her surveyor's fee right then & there! At this point, I was ready to bail on the whole deal (since this was a structural issue) but it was Gail who suggested that we do the sea trial and let her issue a report. We did but when I received her report, I was ready to either cancel the deal or not settle for anything less than a $7k price reduction (other factors were involved too). As it turned out, the broker had already been talking with the buyer and had gotten approval for a $10k reduction! We completed the deal and I rebuilt the bulkhead and surrounding cabinetry for $300 in materials. Since then, we've been in sustained 35kts wind (day prior to hurricane Wilma arrival) on a port tack going to windward and the bulkhead is solid.
The following link shows the rebuild process (note that the chainplate shown in most photos is for the uppers - the backing board was rotted too and was replaced)
Moral of the story: Get a good surveyor, a good broker, and be on the boat for the survey! It doesn't hurt to show "consternation" if something significant comes up - motivates the broker!