“When it comes to helping you, some people stop at nothing” was written in April 1959 by syndicated newspaper columnist Helen Bottel (1914-1999). “When it comes to giving,  some people stop at nothing” (a “charity” version of the line) was cited in print by at least 1962 and is of unknown authorship, although the “General Features Corporation” has been credited.
 
“When it comes to charity, some people will stop at nothing” is frequently credited to comedian Jimmy Carr (born in 1972), but the line ha been a decade old by the time he was born.
 
   
19 April 1959, The Dominion News (Morgantown, WV), “Helen Help Us”” by Helen Bottel, pg. 3, col. 2:
When it comes to helping you, some people stop at nothing.
 
Google Books
The Complete Toastmaster:
A new treasury for speakers
By Herbert V. Prochnow
New York, NY: Prentice Hall Press
1986, ©1960
Pg. 63:
When it comes to helping you, some people stop at nothing.
 
Google Books
When It’s Your Turn to Speak
By Orvin Prentiss Larson
New York, NY:  Harper
1962
Pg. 79:
“When it comes to doing for others, some people stop at nothing.”
General Features Corporation quoted in Reader’s Digest, July, 1960.
 
28 March 1962, Boston (MA) Herald,  “Marge” by Marjorie Mills, pg. 34, col. 3:
WHEN IT COMES TO GIVING, some people stop at nothing,” is a Reader’s Digest quip you collectors for good causes will appreciate.
 
1 December 1962, Alton (IL) Evening Telegraph, pg. 1, col. 2:
TODAYS CHUCKLE
When it comes to giving some people stop at nothing.
(1962 General Features Corp.)
 
30 December 1962, Daily Plainsman (Huron, SD), pg. 4, col. 4:
TODAY’S CHUCKLE
When it comes to giving some people stop at nothing.
 
Google Books
20,000 Quips & Quotes
By Evan Esar
New York, NY: Barnes & Noble Books
1995, ©1968
Pg. 123:
When it comes to giving charity, some people stop at nothing.
       
Game Gossip
Wow, just saw Jimmy Carr live gig
Derek237
11-22-2006, 06:33 PM
(...)
When it comes to charity, some people will stop at nothing.
   
Google Books
Dim Wit:
The Stupidest Quotes of All Time
By Rosemarie Jarski
Berkeley, CA: Ulysses Press
2010
Pg. 313:
CHARITY.
When it comes to giving, some people stop at nothing.
Yiddish proverb