I don't know whether "clientele was" vs. "clientele were" is a question of British vs. American English conventions, but I can tell you I remember staring at that for a long time trying to decide whether the subjunctive applied, and if so, whether "clientele" needed to be treated as a singular noun or a collective one. I'm still not 100% sure! But I ended up going with "was" on the grounds that while "were" may be more technically correct, "was" is correct in colloquial English regardless.
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I don't know whether "clientele was" vs. "clientele were" is a question of British vs. American English conventions, but I can tell you I remember staring at that for a long time trying to decide whether the subjunctive applied, and if so, whether "clientele" needed to be treated as a singular noun or a collective one. I'm still not 100% sure! But I ended up going with "was" on the grounds that while "were" may be more technically correct, "was" is correct in colloquial English regardless.