Looking at the comments above I think we sometimes forget what a freebie is; no company and no brand in the world will ever give you anything for free not getting anything in return. For the brand, offering free sample, means either getting your contact details, or making you like their facebook page, which in turn increases their brand value. So, in other words, when you see a free sample and you decide to enter your details - that contact information is your 'payment' for that product the company sends you. And for that reason, before you start questioning whether it is worth giving out your details for that 1,5ml sample - think how much details you pass on when you buy that same product for £50 using you credit or debit card. ;)
Yeah its just a tactic by facebook + company to give your details to facebook without breaking law of info sharing.
Stay away of Facebook scam! Big Cold!