In 2005, Merk was awarded the German Bundesverdienstkreuz (Federal Cross of Merit) in recognition of his service to football and his charity work in India.

He ended his career by refereeing the match between Bayern Munich and Hertha BSC Berlin on the last day of the 2007–08 Bundesliga season on 17 May 2008.

[2][needs update] In 1988, Merk was appointed the youngest Bundesliga referee ever, aged 25, representing his home club 1.

On 21 April 2004, during a Champions League semi-finals match against former team Porto, Jorge Andrade, Deportivo's defender, was sent off by Merk for a kick on Deco.

[4][5] Another controversial moment came in the 71st minute of a match between Artmedia and Porto on 6 December 2005, when Merk overlooked a handball by Pepe in the penalty area.

He was the referee in the semi-final of the 2003 FIFA Confederations Cup between Cameroon and Colombia, a game remembered for the death of Marc-Vivien Foé.

Merk was highly critical of the whole FIFA refereeing process after that, stating in the German sports TV show das aktuelle Sportstudio, it "robbed me two weeks of my life" being forced to stay in the referee camp without a call-up, and adding a mere two was a bitterly meagre payoff regarding the fact he (among others) had to visit countless seminars and were sent on small junior tournaments all over the world to merely assist, comparing it to as if Ronaldinho would have to agree to sit on the bench for the Brazilian U 20 in order to qualify for the World Cup.

[10] The religious Merk is active helping slums in India, providing basic dental care for the poor since 1991.

He helps the Indienhilfe Kaiserslautern, which erects schools and housing for the homeless, as well as offering basic medical care.