1. Did you sight a flea or flea dust?
2. If you did, use capstar tablet according to weight (it kills fleas very quickly and you can see the dog gets comfortable very soon. The maker is Novartis ) I usually give one a day for three days.
3.I find Comfortis tablets very useful as flea treatment for my dogs. Comfortis works well for dogs with flea allergies etc, but I am hesitant to recommend for older dogs as some reviews indicate averse med reactions. (not specifically for older dogs but younger ones or certain specific breeds) Some other members use Revolution, Advocate, or Frontline. You will find them quite expensive if you try to buy from a pet shop. I use online shops. The dog will require monthly application for spot on drops.
4. You mentioned about those collar and spot on drops from supermarket. Do you think they have receipts, then they can get their money back (they guarantee on their prodcuts-at they used to ) with evidence that they don't work.
5. It is a good idea to apply flea bomb as you mentioned.
It is very nice of you helping them . Let us know how things go. Good luck!!