DWM Luger

[nasded1]

My brother-in-law has a Luger that he is interested in selling, but he doen't know what it's worth. The info I have collected by examination is as follows:
Luger Identification Form
1. "DWM" toggle inscription
2. #28 proof mark (Parabellum web site), GERMANY, and DMANY inscriptions on side of chamber.
3. Squared and knurled toggle knob type
4. no grip safety present
5. stock lug is present
6. 7.65 mm caliber
7. walnut, checkered grip type w/o border
8. thumb safety safe in rear position with "Gesichert" inscribed at an angle
9. s/n "115" "O" series on barrel and in front of trigger
10. 3-3/4" from forward end of extractor to muzzle
11. #4 proof mark (#28 rotated 90 degrees CCW) on left edge of extractor (Parabellum web site)
12. basic front and rear sights
13. magazine bottom plug made of wood w/o markings

1. DWM commercial Luger, 1924-1930?
2. bluing still at 90%+
3. straw colored finish on trigger and disassembly latch at 20%
4. bore in good condition
5. grips in good condition
6. all matching serial numbers on parts (115 "O series" or 15)
7. no s/n on magazine
8. no accessories

Please establish model and year along with value, and notify me if further information is required.
Thanks.