I'll start by saying I bought him off an eBay seller for just 7 bucks, but the seller was not from Hong Kong or China. He was flattened into a brown envelope which might have contributed to his wide, flat head shape.
Besides the ridiculously cheap price, the only things that made me doubt its authenticity were:
1) His tush tag - The writing is faded, smaller, and further away from the stitching. And were the Sinnoh starters released in 2008 or 2006?
Here is a comparison to the tushie on my legit Budew Pokedoll:
2) His beak is a little oddly skewed to one side, and his toes aren't all that defined (don't know if that's normal)
Here are some of his other angles:
He's soft and squishy, and I love him <3 But any help or similar pictures of your own Piplups would be much appreciated!!