By the hour pricing
Well said, Barb. That's the approach I've taken, and my only complications are larger dogs, IE STANDARD POODLES that i'm gradually increasing more than others to be equal.
New dogs are easy, because I'll quote the hourly rate.
My only complications are the new St Poos, or larger doodles, or larger porties...because the hourly price is more than they have been paying elsewhere. But, I try to keep in mind that if it takes me the same time as 2 shih tzus, then they should pay 2x the price & it's ok if I'm not the right fit for everyone & smaller dogs will eventually fill those slots.