Complaint Review: Footlocker

Footlocker site showed availability of a pair of Nike shoes my son selected for his gift. Ordered the pair and in 3 days get an email that the shoes are no longer available and the order cancelled silently. I called and spoke but got no offer of further assistance. 

By accepting the order from me, is FootLocker not obligated to filfill it? Is this a common practice? Does this not make the whole paradigm of online shopping unreliable. I needed to gift these to my son this Friday and unable to do so because of this. Just wanted to let you all know as a fair warning. 

best,

Sri