can proof of blockchain transactions or merit exchanges strengthen the evidence we provide?
Absolutely!
Merit exchanging (or even one way merits), Default Trust (again, either mutual or one way) as well as DT trust, or trust feedbacks occurring in the same 24 hour period (or week in the case of default trust) are all hall marks of alts being used to build up one or more profiles. An example of this can be seen in my thread:
[Investigation] Four users who distrust pooya87, ndnh, aliashraf,gembitz etcOther examples include registration, or last active dates, posting one after the other in threads (usually attempting to join campaigns) - even spelling and turns of phrases can be markers of alts/connections.
Above all actual use of the same wallets, or wallet addresses not just once but on multiple occasions are solid indicators of two or more UID's being alts.
BUT...
Just because alts use the same wallets/wallet addresses/social media accounts doesn't in itself prove anything unto-wards - like most others, I will make alts trust feedback page with neutral trust feed back to advice others.
OTOH, two UID's applying for the same bounty / signature campaigns using the same wallet address (or in some instances sending funds from two seemingly separate wallet addresses to the same wallet address) are proof of ulterior intentions and most investigators will mark these UID's with negative trust feedback.