Why shouldn’t I just buy an amplifying device or PSAP on the internet or over the counter?

YVDW Audiologists-Yolandé in the Plus 50 Magazine2, hearing test
Yolandé in the Plus 50 Magazine (December ’16 / January ’17 edition)
December 15, 2016
YVDW Audiology Wild en Jag Magazine Page 1, hearing test
Yolandé’s Article in the WILD & JAG magazine – April 2017
May 11, 2017