Fleas? help?

Dweezil is now allowed on the couch, so I'm a little more conscious of the possibility of fleas.  She's always been a scratcher, as I assume most dogs are, but I'm not sure when it's supposed to be excessive.  She's always had these black spots on her lower tummy.  I read about flea dirt and such, but when we visited the vet once and I brought it to her attention, she told me that it's something like doggie eczema.  Does that ring a bell with anyone?  The bigger spots, I've pulled a couple off -- the vet tech did, too, and they were scabs ...  I guess this is just my being paranoid?  Does anyone bathe their dogs with flea/tick shampoo each time?  or is that just to be used when you really suspect the little bugs?

oh and PS -- she is on Advantix.