you mean owners of FB with green plate is depriving those with franchise?
yes, if it use for shuttle/delivery not duly registered w/ the LTO for its business utility, not all the time but it happens eventho green plates OTHERS (colorums) tend to use their unit to the max even to the extent of accepting (tempting) offers to transport goods or people (balikbayans prefer this unit) to remote destinations for a certain fee...

but private owner of FB is not there to compete with them to begin with. its for private use.
sir, in your part i believe your intention is honest to goodness vehicle ownership BUT you're not speaking for everybody who owns a vehicle or an FB like you...

granting it is being use for business, does one need to have a franchise to use it as a delivery van?
yes you have to registered that unit at the LTO, franchise to operate if for shuttle service and declaration of "for delivery use" for transportation of goods plus the usual markings of capacity, loads, etc...

i wonder if a colorum put a "not for hire" markings in his FB... will this make him legal or avoid apprehension?
for awhile a colorum can get away w/ this set-up but not for long,
legal if we based our observation on the physical appearance of the unit but illegal and cannot avoid apprehension once asked by a traffic officer on its Certification of Registration and Official Receipt stating its true category - Private or Commercial/Business Use...

HTH!