Spurs were still willing to pay £23m, the installments were spread out over 5 years. The money was still getting paid unless you're saying the deal was £5m and the entire rest of it was based on his behaviour or how he plays? You don't get a new iphone on contract and say your phone is only worth £39 because that's what you had to put down on it.
A phone and a footballer can't be compared the way you're saying. He's our asset, and we'd sell him to use the sale money elsewhere. Would you sell me your phone for a tenner, leave yourself without a phone but be happy to get the rest of the money for it in half a decade? No you'd want the money to spend elsewhere on a replacement, and ten quid won't get you a phone.
Spurs £23m bid had conditions based around Saido's appearances and where they finished in the league. So to use your phone based analogy, would you sell me your phone for a tenner, and I'll pay you the rest of it, over five years, if I run out of texts and call time every month?
For all intents and purposes, if we sold him for £5m up front, he didn't make enough appearances, got injured and his career ended, and spurs didn't make it to Europe, we'd have lost OUR player for £5m. That's appalling business. You cannot claim Berahino is still worth £23m unless ALL of Spurs criteria are met. And NONE of them are in our control.