We would highly recommend this B&B to anyone staying in Florence. The location was only a short walk (5 minutes) from the train station, and very close to the major tourist sights in Florence. Veronica was the sweetest, most wonderful host ever and gave us tips on places to eat (from dinner to pizza to gelato), as well as advice on all the major tourist attractions. The room was very spacious and clean, and although the bathrooms are "shared", they were really very nice: for four suites, there are two full bathrooms with locking doors. The rooms were stocked with large bath towels and the bathrooms had soap and shampoo, which was very convenient. Breakfast is at a cafe next door, and is very good.
The B&B is right next to the San Lorenzo market, which seems to be a combo of open air market (with leather goods, t-shirts, and other trinkets), as well as a covered market with food sellers. This is both good and bad: on one hand, the vendors set up shop pretty early and can be a little loud (there are earplugs provided for light sleepers), but on the other hand the market (both open air and covered) are fantastic to wander around.
I would definitely recommend Residence Martin to anyone who stays in Florence!!!