ACROSS
 1. OUTSOURCE* = COURTEOUS <showing good manners>
 6. <metal> BRASS = BRAS + S_
 9. <view> VISTA = VISA outside T_
10. RATE* SURE _R_ = TREASURER <committee member>
11. <full> REPLETE = RE PE outside LET
12. (WE DON'T)* after L = LETDOWN <disappointment>
13/19. MAI[-n]TAI[-n] = MAI TAI <rum-based beverage>
14. →"COLLIE MODEL"← = MOLLYCODDLE <give too many treats>?
16. C U + TAN DDR IED = CUT-AND-DRIED <without a doubt>
20. ARCH ←CIA← = ARCHAIC <old-fashioned>
22. <ruthless> VICIOUS = ICI inside VOUS
24. <cross> INTERSECT = IN STREET* outside _C_
25. O_ LIVE = OLIVE <green>
26. (.m)EN DO W(i) = ENDOW <fund>
27. <direct attention towards> SPOTLIGHT = ←TH_ GILT OPS←

DOWN
 1. <fill in for> COVER = COVE _R
 2. <crude> UNSOPHISTICATED = (TOUCHED PIANISTS)*
 3. <seller> TRADESMAN = ←NAMED ART← outside S_
 4. M inside O_ A_ TEAL = OATMEAL <cereal>
 5. ELLE inside SHY = SHELLEY <author>
 6. BEST outside E = BESET <plague>
 7. AIRING outside CONDITION = AIR-CONDITIONING <cooler>
 8. (TIGER SEEN)* = SERENGETI <national park>
13. <automate> MECHANISE = (MINES EACH)*
15. <traditional> OLD SCHOOL = O_ LDS CH ←LOO←
17. DU_ + CHESS = DUCHESS <title>
18. VI inside INTRO = IN VITRO <under laboratory conditions>
21. <pointer> ARROW = [-h]ARROW
23. WEPT after _S = SWEPT <won everything>