In my first ever post, which feels like it was written a million years ago but was actually written in February, I lamented the fact that I was waiting for a professional assessment of the Ghost of Ping-Ling, and my wait seemed to be going on forever. It did finally come, about four weeks after I wrote that post. Was it worth it? At the time I thought it was. The assessor made some helpful comments and I acted on them, and I think the book is better for it. But now I think I could have achieved the same result without spending anything like the money I did, and in a fraction of the time.
If you pay to have someone assess your manuscript, it costs approximately $500 for 80,000 words. For that you get a 10-20 page report, detailing everything from plot holes to weaknesses in dialogue, character, grammar etc. You get ONE person's opinion, and they may or may not understand/appreciate/like the genre/style of what you have written.
Looking back over my assessor's report, there were some good and helpful things, like I said. But there was a heck of a lot of bumf as well. Many comments were made that were plainly subjective, objections were raised that demonstrated that the manuscript had not been read with particular care, and occasionally things were said that were so left-field I still don't understand the point that was being made. In fact, there was nothing helpful mentioned that wasn't also identified by friends who read and made comments - and their comments were free (except for bribes like bottles of wine etc).
Another interesting thing: the assessment service I used advertised that if a manuscript was considered "publishable" they would include a letter of recommendation to be passed on to agents and publishers. Of course, now that I read publishers and agents blogs, I discover such letters make not the slightest difference, and get thrown out along with the envelope they came in.
End result? In my (humble) opinion, these assessment services are a complete waste of time and money. It's far better to trust the opinion of friends, and to use online crit-groups like Online Writer's Workshop, which costs hardly anything and exposes your work to lots of informed readers, not just one.
You live and learn. What a difference five months can make.