Ivermectin is much better than a dip from a petstore. Personally I try to avoid any type of dips, shampoos, or topicals from petstores or grocery store unless I'm confident in their safety and efficacy. Most are rather scary and ineffective when you really compare it to what's available these days. Ivermectin is quite safe for nearly all animals aside from a few breeds of dogs like collies that have a particular sensitive to it and it should be 100% effective by the 2nd or 3rd dose. Sometimes a 4th is given in more severe cases or just to be certain. For breeds sensitive to ivermectin or to avoid giving multiple doses every 7-10days revolution can be used instead and only repeated once after 2weeks. Revolution used on the standard monthly schedule will also prevent sarcoptic mange if you have other animals at risk or live in an area where the dogs keep picking it up from wildlife.
10days from the 2nd dose should be safe if your vet didn't feel the need for a 3rd dose.
Scrapings are somewhat pointless. If we include dogs showing minor symptoms they only show positive in 20-50% of cases. 50-80% of dogs with sarcoptic mange will be missed and the more minor the symptoms the more likely it will not show positive on a scraping. We quit doing them when I was in small animal rescue because the numbers are the same for animals like guinea pigs and it's safer just to treat with ivermectin irregardless of the results of a scraping. Personally I'd prefer to do a 3rd dose but if you aren't going to then I doubt waiting a few more days is going to do any good. The ivermectin has killed what it's going to kill so the only way you'll know if it got everything is if symptoms get worse instead of better over the next week or 2 or if you had a positive scraping that proved it wasn't completely effective. Ivermectin does not kill all life stages of internal or external parasite which is why you have to repeat it around the time the eggs would hatch or larvae would mature so you can kill the next round of adults before they lay. The 3rd dose or possibly 4th is just in case your timing was off and you missed a few that weren't in a stage they could be killed.
The other option like I said is revolution. You can get a couple months supply for all dogs you plan to have in the house and use it monthly until you know they are clear. It is one of the more expensive monthly topicals but it also prevents heartworm and kills several other common internal parasites so it can take the place of your heartworm medication, dewormer, mange treatment, flea, and tick preventative.
