Last summer, Tottenham signed five players, two of whom – Victor Wanyama and Moussa Sissoko – were already playing in English football.
While Wanyama, a £9million signing from Southampton, has had an outstanding season, Sissoko has been a huge disappointment following a move from Newcastle that could be worth a club-record £30m.
Vincent Janssen, Georges-Kevin Nkoudou and goalkeeper Pau Lopez have made little or no impact.
This summer, Tottenham are expected to move for Crystal Palace winger Wilfried Zaha and midfielder Ross Barkley of Everton, but Pochettino acknowledged: "There is a good reason [to sign Premier League players] but it’s not easy to find the right player for us in the English market.
"Sometimes you need to guess, and sometimes you need to compete with different clubs who want the same player as you. It is not easy for us.
"In the English market, it is difficult to find the right profile of player to add, and when you sign players from other leagues it is always a big question mark."
Tottenham pay lower wages and are more careful in their transfer spending than the other teams in the top six, as Pochettino conceded.
He said: "Sometimes it is the situation that you cannot compete with another club. That is something everyone knows. But I think we are strong because we are a team.
"When good players make up our team, we are very strong. The names are not important, because when we don’t play as a team we are weak.
"This season you can see many examples of different players in different games, where we have won some and lost some.
"So our focus in on players who want to be part of the project, and feel they need to play in a certain context.
"They need to be willing to train hard and show the disciplinary standards that we set."