We haven't got hands on with these as yet, but we've got reasonable expectations for the first Secondhand & Vintage City Guides by Vivays Publishing.
The two initial volumes on the market are Secondhand & Vintage London Andrew Whittaker and Secondhand & Vintage Berlin by Delia Dumitrescu. The London volume covers 160 pages, promising 'an insider's guide' to the best shops and markets, broken down into sections and address details plus a brief description of the shop or stall. The second part of the book is organised by area, colour coded to the types of objects they sell, with a further section featuring info from both shop owners and locals about the areas. 'Hidden gems' as they call it.
The Berlin book? Well, according to the write-up, it has the same number of pages and the same layout, but with Berlin information substituted for the London stuff.
If you are new to either city, might be worth picking up to get you started. Other books are likely to follow too, but in the meantime, you can pre-order both of those volumes, both selling online for £8.06 each.