Tottenham Hotspur’s transfer activity this summer has taken just about everybody by surprise.We are not talking only about spending nearly £250million on six new signings, breaking their transfer record twice in the process with the arrivals of Mateus Fernandes and Sandro Tonali from West Ham United and Newcastle United respectively, but also making strategic sales.Chief executive officer Vinai Venkatesham has spoken publicly on multiple occasions about how Spurs need to improve at selling. Real Madrid, Chelsea and Manchester City are the best examples of top clubs who are unafraid to cash in on their young talent and reinvest the fees received into the first-team squad.Luka Vuskovic was 16 years old when Tottenham agreed to sign him from Hajduk Split in his native Croatia. Vuskovic officially moved to north London only last summer after turning 18, then spent the season on loan with German side Hamburg.The centre-back’s £46million transfer to Brighton & Hove Albion in July feels bittersweet, as he never made an official first-team appearance for Spurs, but that money represents a significant profit on the £12m they paid for him. The 19-year-old has no Premier League experience, and would have been stuck behind new signing Jan Paul van Hecke and Kevin Danso for playing time in the right-sided centre-back spot.Vuskovic is this summer’s headline sale, and the third biggest in the club’s history behind Gareth Bale and Harry Kane, but Tottenham have extracted value from other players on the fringes of their first team.Will Lankshear joined Middlesbrough of the Championship last month in a deal worth £10million, with another £10m to possibly follow in add-ons. Ashley Phillips, who has spent the past two seasons on loan to Stoke City in that same division, is following Lankshear to the Riverside Stadium for an initial £7m, which could rise to £20m.Alejo Veliz and Alfie Devine have moved permanently to Brazilian side Bahia and the Championship’s Preston North End respectively, while 18-year-old winger Tynan Thompson joined Manchester United for up to £8m.Spurs have inserted sell-on clauses into most of these deals, and have matching rights for Vuskovic, Lankshear and Thompson.Those six players had a combined total of less than 20 senior appearances for Tottenham, but if you add all of their fees together, they cover a significant chunk of the club-record £100million they are paying Newcastle United for Tonali.Vuskovic’s value skyrocketed during his loan at Hamburg (Selim Sudheimer/Getty Images)In an ideal world, these players would become first-team stars at Tottenham, but it is not always possible. Sometimes, letting young talent leave is right for all parties.Spurs have not always sold well when it comes to academy players who don’t become senior squad regulars.Over the past five years, their best deals of that kind were Cameron Carter-Vickers’ move to Scottish giants Celtic and Troy Parrott’s €8million (£6.9m/$9.2m at the current rates) sale to AZ of the Netherlands. Last summer, the only significant departure was Josh Keeley’s £1m switch to Luton Town of third-tier League One.It is no coincidence that they have raised a lot of money offloading youngsters this summer. Considered and sometimes bold decisions have been made about their development by head of loans and pathways Andy Scoulding and academy director Simon Davies, which have finally come to fruition.Vuskovic spent time on loan with Polish side Radomiak Radom and Westerlo of Belgium as well as Hamburg. Westerlo were viewed as a good opportunity because they play top-flight football but do not attract a lot of attention. Vuskovic could make mistakes and grow without intense pressure. There was a huge emotional draw for Vuskovic to join Hamburg — his older brother Mario is contracted to them but is serving a doping ban until this November — and it was seen as a natural next step in a more competitive environment.