Mixing breeds, the so-called designer breeds, can be a disaster...
I cannot believe the popularity of the "Labradoodle". Almost without exception, in the last 4 years, every Labradoodle I have dealt with (maybe two dozen), have had hyper, agitated temperaments. Hyperactivity from the lab, intelligence from the poodle, and not mixed in a good way. Most of these dogs have required extensive training, are much more demanding of attention than most other dogs, and in the wrong owners hands, they have been a disaster. Labs are great, poodles are great, mixing them is not...
If you're shopping for a true teacup dog, make sure that you are not being shown/sold tiny 5-6 week old puppies. At this young age, puppies cannot make eye contact and cannot follow your finger back and forth in front of their faces. It's not until right about 8 weeks that they are capable of following your finger back and forth, and to look you into the eye. They should also be eating solid food...
If I had a dime for every unknowing person that I have met in my career that has been sold a teeny tiny unweaned or force weaned 5 week old puppy (usually Yorkies or Poodles) as a "teacup" (only to have it grow into a full sized 6-8 lb. dog), I could afford a vacation in the Bahamas...!
If investing in a true teacup puppy, make sure to do your research and be prepared for blood sugar issues until they get over 2lbs. It's very, very common...
Here's a pic of my 3lb. Blue Merle Chihuahua, Inky. He is 5" tall (that's a 8" teacup collar with the smallest ID tag made)....