The experiences and advice recounted by Shyheels make a great deal of sense. It is certainly better to seek the consent and co-operation of an intended 'subject' before openly taking film or photos. It can pay dividends, as he demonstrated.
However, that is not very practicable (and may well be inadvisable or pointless) when a candid, arguably intrusive or spur-of-the-moment shot is needed - and I guess that most street shots of footwear fall into that category. A discreet (OK - arguably furtive) approach is needed in most such situations - the subject will probably have neither knowledge nor concerns about being photographed and will move on, none the wiser. Let's face it - if one wants that particular pic, it is going to get taken regardless of the subject's possible (indeed, probable) objections, based on an an assumption of a pervy interest.