Uncle Sam welcomes more reliable loan sharks (7)
I believe the answer is:
usurers
'loan sharks' is the definition.
('usurer' can be a synonym of 'loan shark')
'uncle sam welcomes more reliable' is the wordplay.
'uncle sam' becomes 'us'.
'welcomes' means one lot of letters goes inside another (in sense of 'invites in').
'more reliable' becomes 'surer' ('sure' can be similar in meaning to 'reliable').
'us' placed around 'surer' is 'USURERS'.
(Other definitions for usurers that I've seen before include "They charge excessive interest" , "Biblical bankers who overcharged" , "Loan sharks" , "They lends money at excessive rates of interest" .)