Here are the facts.
In the 2009/10 mercato, Tare spent 31.5 million on Zarate (20), Eliseu (1), Matuzalem (6.5), Barreto (3), and Hitzlsperger (1), all of whom eventually flopped at Lazio.
In the 2010/11 mercato, Tare spent 9 million on Floccari, who also flopped with the Biancoceleste.
In the 2011/12 mercato, Tare spent 17 million on Stankevicius (2), Konko (6), Cisse (6), and Alfaro (3), all of whom flopped at Lazio (except for Konko, but I'd argue that the Frenchman has generally been mediocre, hence why his starting berth has been displaced by Cavanda).
In the 2012/13 mercato, Tare spent 4 million on Ciani, who also flopped at Lazio.
In the 2013/14 mercato, Tare spent 19 million euros on Biglia, Anderson, and Perea, and he undoubtedly overpaid here. Don't forget he was demanding over 30 million from PSG for Hernanes, but eventually sold him for half that value (only reaping a 5 million profit from his sale over the original transfer fee paid by Lazio to Sao Paulo in 2010)
Throwing away 80.5 million euros over 4 years at a club as frugal and economically weak as Lazio is surely poor business.