Learn English – “this is A big but…” or “this is THE big but…”, any difference? which is correct

articlesusage

But, and this is A big but here, all of this can be purchased out on the black market.

But, and this is THE big but here, all of this can be purchased out on the black market.

After I google, there seems to be more results for "this is A big but…".

But, and this is A big "but" here, all of this can be purchased out on the black market.

There could be more than one "but", either earlier in conversation or later.

But, and this is THE big "but" here, all of this can be purchased out on the black market.

There isn't going to be any bigger "but" than this one in this sentence.