A proper stock counter on the website linked to the warehouse/stockroom database- no BS about what's in stock and no more issues with website info not corroborating with stock level.
When it comes to customer service, one little thing I like to see is a picture of the complete order sent to me when it's been picked out of the warehouse. Flecktarn.co.uk are the only retailer I've used who do this, and it's quite reassuring to know what's happening in terms of hours rather than days.
An info section recommending what to and what not to buy as a new player would help people starting airsoft- it wouldn't harm business but there wouldn't be issues with breakages and returns when newer players buy GBBRs or sniper rifles which aren't suitable for beginners. It would make it much easier for them than having to fish around on the internet.
Package deals for rigs would be good too. I'd like to see bulk deals on magazine purchasing where possible too, buying a new set of mags can be very expensive after purchasing a new gun.
But I would definitely like to see a proper all-in-one customisation service- laser engraving, hydro dipping, custom sewing, custom guns put together- this would make you stand out as a retailer. It would set you apart more than a normal retailer offering spring changes and parts installation.