Next Step is great for over two three decades now.but my advice is that go to kennels only when you are planning to show your dog,or else its a complete waste of money. my advice ------
1) go direct to the kennels,not through middleman
2) check the parents of the pup live not through pics
3) look for a broader nose,broader nose means broader muzzle
4) dont go for oversize boxers,they are more prone to joint problem.as boxers are supposed to be meidium size dogs,and there is no size disqualification in show.
5) flashy or white marking gives beauty to a boxer but is u are showing then white should not be more than 1/3 of the base colour
6) best price varies like a brand has guarantee,but only for show purposes otherwise proper identification of the pup and parent might be enough for some.
7) the person breeding must have ample knowledge and experience at breeding boxers.