I picked up booklets of the German colonies not long ago, and I actually found the advertisements to be more fascinating than the stamps. How sad is that?!?
Three German colonies (
German East Africa,
German Southwest Africa,
Cameroon) issued stamps in booklets. Each issued three major varieties (Michel MH1, MH2, MH3), with each major variety having two sub-varieties (
A and
B). German Southwest Africa added one final variation of the third series (MH3 II) in 1914.
The early booklets (Michel MH1 and MH2) and the late DSWA variation (MH3 II) are very rare, with complete booklets cataloging for 6,000-7,500 EUR. You won't be seeing any of those here today!

Instead, I'll use the
German Southwest Africa MH3 I B for show and tell. The "I" denotes the mid-1913 issue, as opposed to the rare 1914 issue ("II"). The "B" denotes the sub-variation with perforation that doesn't go through the margin of the stamp panes.
Because I shrank the photos for posting, some of the text of the ads is hard to read. So, the photos are hyperlinked to where I have the hi-res versions posted.
The cover shows the contents of the booklet -- twenty 5-Pf stamps (Mi 25) and ten 10-Pf stamps (Mi 26), for a total price of 2 Mark.

DSWA MH3 I B Front Cover
The inside cover shows our first ad -- for Dr. Theinhardt's Nutrients Society, selling hygiama in powder or tablet form, as well as his own form of baby food.

DSWA MH 3 I B Inside Front Cover
Next is the first pane of stamps -- 6x 5-Pf
Hohenzollern issues.

DSWA MH 3 I B Stamp Pane 1
Next is an ad for Pelikan ink ribbons and the Charles Tauber Photographic Mail Order House.

DSWA MH 3 I B Ad Pane 1
Next is a second pane of the 5-Pf issues.

DSWA MH 3 I B Stamp Pane 2
The next pane is an ad for Schwetasch & Seidel, manufacturer of fine cloth for men's and women's clothing.

DSWA MH 3 I B Ad Pane 2
The next pane is yet another of the 5-Pf panes.

DSWA MH 3 I B Stamp Pane 3
The next pane is an ad for Patent Baueneisen Construction, featuring cheap iron construction that withstands tropical storms, fire, and termites!

DSWA MH 3 I B Ad Pane 3
The next pane of stamps features the remaining 5-Pf values, and the first four 10-Pfs.

DSWA MH 3 I B Stamp Pane 4
The next ad is for Kalisyndikal (Potash Syndicate) in Berlin. Judging by the font size, they're really proud of their potash.

DSWA MH 3 I B Ad Pane 4
The final pane of stamps contains the remaining 10-Pf issues.

DSWA MH 3 I B Stamp Pane 5
The final ad pane is for the Dihlmann Brothers shoe factory in Tuttlingen, and the August Dürrschmidt musical instrument company.

DSWA MH 3 I B Ad Pane 5
The inside of the back cover features an ad for the Baer Brother's "health cigars", recognized as world champions and gold medal winners! Patented in 14 states, and recommended by doctors!

DSWA MH 3 I B Inside Back Cover
And finally, the back cover, featuring an ad for Burgeff & Co, the Rhein's oldest sparkling wine cellars.

DSWA MH 3 I B Back Cover
The ads are the same in all three colonies' MH3 varieties. They're different in the MH1 and MH2. If I ever win the lottery, maybe I'll share those with you as well.