being blackmailed

[awesomeacaciaaustralis]

Hi I've a buyer that brought a item and I also gave him a sample to try as it was a better quality product ,, now he wants compensation to pay for the processing of the sample I gave him and he keeps throwing the feedback over my head at first I compensated him 1 time already even though I didn't have too but I've worked long and tirelessly to have my 100% feedback and a top rated seller and power seller aswell and I'm feeling blackmailed is there a way to deal with these types of ppl before they give you a neg FB anyway