Best on Key West did not stand behind 110% low price guarantee Key West, Florida

we used this service to book an all-inclusive water 'adventure' in Key West.  They advertised a 110% low price guarantee.  We paid $109 per person (4 of us) plus an additional $30 to parasail for each person.  The couple in front of us paid only a total of $20 each for the same activities as we were allowed to partake in, except for parasailing.  This was a price difference of $89 per person or a total of $356 dollars for our party of four.  We were told by the Best of Key West upon notification of this price difference that this couple were "relatives of the owner" and were given a FREE tour and that their $20 charge was for taxes and fuel.  I believe this company should have stool behind their WRITTEN price guarantee, no matter if the couple was family of the owner or not.  A guarantee is a guarantee!!!  It makes so sense to me that the owner would charge his family members for tax and fuel.  Seriously????