Hardcoding - seth blinding using network id as chain id, getting invalid sender error

**Issue by [thapakazi](https://github.com/thapakazi)**
_Wednesday May 16, 2018 at 13:17 GMT_
_Originally opened as https://github.com/dapphub/seth/issues/36_

----

Just thinking out loud, how safe is it to simply assume networkID and chainID same.
Stumbled upon here because I was using different chainID and netwworkID, and seth was just throwing out `invalid sender` error.

Turns out we have been setting chain-id.
https://github.com/dapphub/seth/blob/aae347d3a5bba435b41b7fed7cc8116ab2bc4a81/libexec/seth/seth-mktx#L18

It would be better if we have a option to send the chain-id param explicitly and set `rpc net_version` as default like:
```
--chain-id ${chain_id_from_option:-(seth rpc net_version)}
```

Thoughts ?

Start by inspecting libexec/seth/seth-mktx at the referenced line where the chain ID is selected. Trace how seth rpc net_version and command-line options are handled, then verify that an explicit chain ID can be supplied while the network ID remains the default when no option is given.

Written by the indexing model from the issue text.