How to best utilize DTAs depends a lot on where you live and you should speak to a lawyer or accountant in your country to ensure that you get 100% accurate advice.
However, the most important note is that
Seychelles, Belize, and BVI have signed relatively few DTAs.
Seychelles: 23, Belize: 12, and BVI: 1. Compare this to some of the low-tax jurisdictions in Europe: Malta (67), Cyprus (45), Luxembourg (73), and Switzerland (96).
While DTAs are normally used to ensure that if you pay tax in country A you only pay the remaining difference in country B, there are cases where paying tax in country A is enough, depending on what type of income it is (salary,
dividends, profits from sale, et cetera).
What's quite unique about Malta is that the corporate tax is among the highest in the world: 35%, but you can get a refund of up to 100%, though normally just 88%. I have seen people get away with declaring this 35% tax rate to their home country and thus be free from tax, and then afterwards getting the 88% refund or shifting the refund to another legal entity, which then re-invests into the Maltese company. These things vary a lot between countries and if you want a legal, low-tax structure, you need professional advice.