I found an answer, I know I'm a little late but it could well be useful to others who have the same issue:
attempt to buy the weapon, but don't accept or confirm the deal; instead look at the trade offer and go to the bot's profile page and then their backpack. You can then search for the weapon and use the inspect in game button from there. This should work considering the steam market uses the steam client for an inspect-in-game button, and scrap.tf doesn't open Steam.
edit: If you wanna test out some war paints, some community servers have commands to allow you to equip any war paint on the acceptable weapons but bear in mind if anyone tries to use this tip that it isn't an accurate command (e.g. if you wanted to use a white tiger buffed weapon for yourself the command will just give you the standard colour, and if for whatever reason you like scratches and blood it won't be insanely accurate but will hopefully give you a general idea of what the weapon will be like.)