Is there a better term to describe second hand dealers (for electronic devices) and second hand dealers (for collecting newspapers and magazines for recycling)?
"Second hand" goods are goods that have been previously owned. In the USA, "used" is more frequently used.
If the goods are old enough and in good enough condition, they may be considered "antiques".
When these are sold in shops:
There are also "antique shops" and "antique salesmen", if the goods are actually antique (although sometimes the definition is pushed somewhat).
In recent years, particularly for good quality second hand clothes of some age, the word "vintage" has come into use. "Vintage clothes shop", or just "vintage shop".
In the UK at least (and, to my knowledge, everywhere else) "second hand dealer" is not generally used when the goods are to be recycled (as opposed to re-used whole).
So, I would use "second hand dealer" to describe someone who buys and sells used electronic equipment.
I would not use "second hand dealer" to describe someone who buys and sells newspapers for recycling. Perhaps a "recyclable waste dealer", if they are selling on to whoever does the actual recycling.
Second hand dealer is the best word that can be used in your scenario. The only other word that I can think of is:
Only thrift shop can be found in the dictionary
I believe the best the word-choice for you is the one that you stated (second hand dealer), since there is no other synonym.