Let's begin the discussion of this question with the statement that you have already decided on the choice of the breed - bullmastiff - and know who you want - the male or female.
In order to avoid later disappointments, which are almost inevitable, if you decide to buy the first caught, albeit unusually cute puppy, you should at least in general terms get acquainted with the exhibition breed of the breed that exists today.
To begin with it is worth to visit several exhibitions. But even after visiting several exhibitions it can be quite difficult to determine the specific type of dog that you would like to buy yourself
In order to make the right choice of puppy bullmastiff , you need to consult a specialist. An authoritative expert does not necessarily have to own a large nursery. This is a person whose interests go beyond breeding puppies just for the sake of money. His (her) advice, for starters, regarding the choice of producers from those who already have puppies, and then (and this is highly desirable) and regarding the choice of a particular puppy from a certain litter, would be very important.
And so, the advice is received, the litter of the corresponding age is picked up, and the time for the examination of the puppies comes.
Experienced buyer with doubt would have reacted to the advice of a "specialist", which blackens everyone and everything, except for himself and his own dogs. Just as I would suspect in the uncleanness of the breeder who, under any pretext, refuses to show all the litter. Situations can be very different: for example, the breeder could already select several puppies from the litter for their friends, relatives and so on, but a decent seller must show all the litter.
The same goes for refusing to show the puppy's mother. Indeed, without this it is almost impossible to judge the future growth of puppies , type and temperament. It is clear that the bitch after childbirth can look far from the best and that even after one or two months it will not recover, but its type, exterior, character and movements from this practically do not depend.
If the bitch in your presence feels insecure, strains, trembles, podimayet tail and hides between the legs of the owner, and released, hiding in a hurry in an enclosure or other room, it should be said that from there you need to leave. In her house, when her puppies are near (which, of course, must excite the dog up to open aggression), in the presence of its owners, a normally educated dog is simply obliged to behave defiantly.
Or, at least, confidently, even if somewhat a little excited. Unfortunately, very often cowardice is inherited. In the end, it's about dogs that will be required to protect you from a real attack. That is, with an aggressive dog (knowing its potential capabilities) from puppyhood can work and, as a result, really learn how to manage it. With a coward there will be nothing to do. From it is unlikely to be a brave dog.
Cowardly behavior for bullmastiffs is not typical. If a bitch or a male (producers) are cowardly - buy a puppy from this pair. The coward in the house is not a joy, a complete chagrin and humiliation.
If the bitch you selected already had puppies, then ask the breeder to show them. Or give the addresses and phone numbers of their current owners. Then you can make your own impression of the type that this bitch transmits.
Do not agree to buy a puppy, which was taken away for you by the breeder himself, without seeing him and his littermates.
So, you are inspecting the puppies. To begin with, the main question should be answered: male or female? There are cases where among the puppies of the selected litter there are only bitches or only males. So, perhaps you will have to make a decision based on the circumstances. If your decision to have a puppy of a certain sex is final, and in the examined litter such is not present - stop examination. Do not worry in vain neither the bitch, nor the puppies.
Bullmastiffs are characterized by a pronounced dimorphism, that is, males differ significantly from females in size, appearance, etc. Dogs certainly look more advantageous than bitches. But bitches are often smarter, more compact and more accurate. True, twice a year they have pustovki (estrus), which is associated with various problems.