The Tau 7 is a well respected target pistol, and runs of C02 capsules (IIRC around 70 shots). Very good as a start up pistol, fully adjustable sights and the one for sale also comes with spare rear and front sight blades. The barrel and rear weights are also included. The large CO2 transfer bottle is also included, but most folk do not use that because you would need a bulk fill to fill that (and suitable adapter). Very nice trigger and adjustable velocity.
They normally go for around £250 (without the bulk fill tank and spare sight blades), so providing that is working well it seems a good buy. However one thing I noticed it that the one for sale does not have an adjustable palm shelf. Therefore I am not sure which model this is (all others I have seen have an adjustable palm shelf). It would be better if you could try before you buy or at least ask what size the grip is (S/M/L).
Spare seals etc... can be obtained Sureshot in the UK. I had a problem on my Tau 7, the o-rings on the piercing cap kept getting damaged, but I resolved this using polyurethane seals instead of the OEM seals. Also make sure the catch on the loading gate is not worn otherwise it will fly open when fired and the breach o-rings will ping out!