recently i have seen many senders asking for drops with login access as they wanted to use it for ach transaction while i see drops says straight no for login access.. so my question is what sender can do if he have online access and account is empty?

Well this is a catch-22 situation!!
A sender needs the online access to deposit the echeck or add funds with cvv (exchanger logins), etc, but with the online access, he can load and rip by transferring the loaded funds he loaded to another account he has the full and only control of and leave you empty and dry!! That's why some drops refuse to give login...the solution is escrow!
If loader needs online access, loader should deposit escrow to prevent or mitigate ripping ...if loader can load without login, then drop should deposit escrow to limit ripping
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what if loader is saying to change ur password in 15 minutes after connecting account? what he can do in 15 minutes?

He will add accou he bro the drop and make transfer

Mostly banks require SMS for every transactions. Even if he add his phone you will receive SMS to confirm the change. So if he want only to watch balance then it is ok to give access to him.