You got to keep mind though that just cuz a dog is skinny doesnt mean its abused.
some dogs are just like that. a dog my mom had for example was a skinny dog but yet was healthy an always had access to food when ever she wanted since she wouldnt over eat. Kribys also on the skinny side. can feel his ribs an back bone when ever you pet him but hes always been that way. ive even tired fattening him up with different kinds of treats an etc.

if the dog eats like a horse an starts packing on the pounds though thats a different matter. id raise an eye brow at that too an keep the dog if i could.