There have been many debates as to the accuracy of German kill claims (for that matter, all kill claims by all nations), especially since the highest scoring Allied ace had "only" 60 confirmed kills...this palls in comparison to the German aces, of which over 100 claimed more than 100 "kills"...I believe conventional wisdom in almost all circles is that all "kill" claims have a degree of inflation...There are some German pilots, however, whose log books can be (and have been) cross-checked with Allied loss records and match fairly well for the most part...two German aces who I have studied and whose records have been combed over by many historians are Marseille and Schnaufer...
Schnaufer had 121 kills, all at night, and most against four-engined British bombers...when you calculate the number of men involved in his kills (at around 7 per kill), Schnaufer may be responsible for more casualties in air-to-air combat than any other pilot: roughly 850, either killed, wounded or made a PoW...
Marseille's logbook also can be verified, for the most part, against Allied loss records, but not completely--there are some real problems with his claims as well, eg:
15 September 1942
JG27 escorting Stukas intercept the attacking fighters and are awarded 19 Victories. 11 by I Gruppe, 1 by II Gruppe, 7 by III Gruppe
However, the P-40's intercepting this Stuka raid were put up by 239 Wing, 36 Kittyhawks from 250 Sqn , 3 RAAF, 450 RAAF, 112 Sqns . Only SIX Kittyhawks failed to return, one which was claimed to be shot down by friendly AA Fire. (2 losses from 250 Sqn, 2 from 3 Sqn, 1 each from 450 & 112 Sqns)
12 Oct 1941
Allied losses, 2 P-40's were shot down, 1 crashed on landing, 1 crashed inside Allied lines.
4 kills were awarded, 2 to Marseille, 1 to Sinner & Franzikest
30 Oct 1941
Allied losses of 2 P-40's and 1 damaged
4 kills awarded, 3 to Schulz, 1 to Schacht
22 May 1942
1 P-40 shot down, 1 missing and 1 crash landed at base.
5 kills awarded.
1 June 1942
1 P-40 shot down, 1 damaged
3 P-40's claimed, 1 Hurricane claimed despite not being present.
3 September 1942
2 P-40's shot down, 1 crash landed at base.
6 kills awarded, 3 to Marseille & 3 to Stahlschmidt (including a Spitfire, not present)
5 September 1942
2 Spitfires shot down, 1 P-40 shot down and 1 damaged
9 Kills awarded, 4 (All P-40) to Marseille, 2 to Stahlschmidt and 3 to Rodel
15 September 1942
5 P-40 shot down and 1 shot down by own LAA
7 kills for Marseille, 4 to Krainek, 3 to Schroer (incl Spitfire)2 for von Lieres and singles to Homuth, Bornger, Grube & Stuckler.
Then there are some of the stories that still circulate about aces who are charged with false claims. One of the more famous incidents involved the beloved Galland who made a solo sortie across the channel and reported upon landing that he was putting claims in for 2 Spitfires...imagine his crew-chief's surprise when he discovered that the plane's guns had not even been fired...oops...