This ^ ... all hotels can have bed bugs, so I'd throw that consideration out the window. I travel a bunch for work (and am a hotel snob to boot) and there's just no way to know about bed bugs ahead of time, so don't worry about what can't be controlled. The Rodeway Inn to the Ritz Carlton can have bed bugs, it's what they do about an infestation that matters. And despite what anyone tells you, there's nearly no way to determine if any are present ahead of time. You can look for stains, look for the bugs themselves, look for bite marks, etc., but the only way to positively ID one is to snatch a bug or its eggs and look at it under a microscope, something that's a pretty tall order.
I have no experience with the Castle Inn but doubt it will be as bad as it's made out to be honestly. Sounds and looks (from online pics) like an inexpensive place to rest your head at night, which is pretty much what you were going for, right?
I agree with a previous poster that if it really bothers you (talking to the OP here), you can almost certainly call the third party agency and ask to be rebooked. EVERYTHING -- and I do mean EVERYTHING -- in the world is negotiable and if you ask nicely I'd bet they'll accommodate you. Maybe with a small rebooking fee or what not but it's a business and it's in their best interests to have happy customers. When asking for concessions, special bargains, or things that are "technically" not possible, the key is to explain the situation to hopefully garner some sympathy, be nice, and implicitly suggest that it's in the other party's best interests too. I've seldom seen a situation where that doesn't work ... applies to rebooking airline tickets, renewing DLR APs at previous prices

, medical insurance denials of coverage, Ticketmaster, pretty much anything under the sun, trust me
I do agree with Mr. Snappy that you get what you pay for though. Perhaps the particular post on the matter was a bit terse, but I think the gist is legitimate. The point is to head in with the right expectations and you'll be fine ... pixiewings71's post on the service issues encountered are indeed a bit disheartening,
but service is honestly the most hit or miss part of any hotel stay, restaurant experience, and so on. If that had happened to me, I would frankly also swear off the property for life. But there's no guarantee it'll happen to you. I'd say to not worry about it and focus on the fact that you'll be enjoying DLR soon and will have a place to sleep and re-energize, however basic it may wind up being. Hey there's a lot worse in life that can happen than going to DLR and staying in basic accomodations, right?