However, if you've got any inkling that all isn't well, then you should wait until you know what it is and have fixed it. I've sent work out that I've had a nagging suspicion wasn't quite right, and hoped that magically someone wouldn't notice but sure enough, it's come back with feedback that nails my nagging suspicion.
I also think you shouldn't send out if you've only just finished writing. Leave it for a week - a month if you can bear it - and then have a read. The longer the gap between writing and reading, the more you'll be able to see it with new eyes. When I do publicity for a new book it's usually been a year since I've last really looked at it, and boy - can I see things I'd like to change! Too late, of course, to do anything about it, but it's taught me that you really do see more if there's a long gap.
But if you've left it, come back and done another edit, and now you're sick to death of it - send it out. A half way house is to send it to friends or even to buy in some professional feedback. But get it out there and see what feedback you get. It's the only way you'll know.