Visited preferred 411 for the first time and noticed the ads. Many of the providers listed their donation followed by a + sign. How is one to know what the true number is?

you can always cross reference with their website and ter profile.

couldn't hurt

Possibly she offers a premium service and charges extra, say for a trip to the greek islands. If all the ads are this way, I do not have a clue.

It's possible that she only gives her rate for one hour, but multiple hours are available at a reduced rate. The other possibility, as mentioned, could be that it's only a base rate, and she charges extra for particular services. My guess would be the second one.

Personally, I would go with a lady without the "plus sign".

I would say it's a premium service (greek) or the girl travels.  Donations will often change and as a person tours as expenses and markets change throughout the US.  My incall rate changes as well.  I would check with her website and/or send her an e-mail.

If you like the girl, and you obviously do, send her an e-mail and ask before you completely dismiss her.  It may be a very simple reason like I posted below.